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Reverse transcriptase
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Reverse transcriptase
(RNA-dependent DNA polymerase)
Crystallographic structure of HIV-1 reverse transcriptase where the two subunits p51 and p66 are colored and the active sites of polymerase and nuclease are highlighted.[1]
Identifiers
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RVT_1
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PF00078
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CL0027
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IPR000477
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PS50878
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1hmv
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1hmv
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cd00304
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RNA-directed DNA polymerase
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2.7.7.49
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9068-38-6
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A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. It is mainly associated with retroviruses. However, non-retroviruses also use RT (for example, the hepatitis B virus, a member of the Hepadnaviridae, which are dsDNA-RT viruses, while retroviruses are ssRNA viruses). RT inhibitors are widely used as antiretroviral drugs. RT activities are also associated with the replication of chromosome ends (telomerase) and some mobile genetic elements (retrotransposons).
Retroviral RT has three sequential biochemical activities:
(a) RNA-dependent DNA polymerase activity,
(b) ribonuclease H, and
(c) DNA-dependent DNA polymerase activity.
These activities are used by the retrovirus to convert single-stranded genomic RNA into double-stranded cDNA which can integrate into the host genome, potentially generating a long-term infection that can be very difficult to eradicate. The same sequence of reactions is widely used in the laboratory to convert RNA to DNA for use in molecular cloning, RNA sequencing, polymerase chain reaction (PCR), or genome analysis.
Well studied reverse transcriptases include:
HIV-1 reverse transcriptase from human immunodeficiency virus type 1 (PDB: 1HMV) has two subunits, which have respective molecular weights of 66 and 51 kDa.[2]
M-MLV reverse transcriptase from the Moloney murine leukemia virus is a single 75 kDa monomer.[3]
AMV reverse transcriptase from the avian myeloblastosis virus also has two subunits, a 63 kDa subunit and a 95 kDa subunit.[3]
Telomerase reverse transcriptase that maintains the telomeres of eukaryotic chromosomes.
Contents
[hide]
1 History
2 Function in viruses
2.1 Process of reverse transcription
2.1.1 Retroviral reverse transcription
3 In eukaryotes
4 In prokaryotes
5 Evolutionary role
6 Structure
7 Replication fidelity
8 Applications
8.1 Antiviral drugs
8.2 Molecular biology
9 See also
10 References
11 External links
History[edit]
Reverse transcriptases were discovered by Howard Temin at the University of Wisconsin–Madison in RSV virions[4] and independently isolated by David Baltimore in 1970 at MIT from two RNA tumour viruses: R-MLV and again RSV.[5] For their achievements, both shared the 1975 Nobel Prize in Physiology or Medicine (with Renato Dulbecco).
The idea of reverse transcription was very unpopular at first, as it contradicted the central dogma of molecular biology, which states that DNA is transcribed into RNA, which is then translated into proteins. However, in 1970, when the scientists Howard Temin and David Baltimore both independently discovered the enzyme responsible for reverse transcription, named reverse transcriptase, the possibility that genetic information could be passed on in this manner was finally accepted.[6]
Function in viruses[edit]
Reverse transcriptase is shown with its finger, palm, and thumb regions. The catalytic amino acids of the RNase H active site and the polymerase active site are shown in ball-and-stick form.
The enzymes are encoded and used by viruses that use reverse transcription as a step in the process of replication. Reverse-transcribing RNA viruses, such as retroviruses, use the enzyme to reverse-transcribe their RNA genomes into DNA, which is then integrated into the host genome and replicated along with it. Reverse-transcribing DNA viruses, such as the hepadnaviruses, can allow RNA to serve as a template in assembling and making DNA strands. HIV infects humans with the use of this enzyme. Without reverse transcriptase, the viral genome would not be able to incorporate into the host cell, resulting in failure to replicate.
Process of reverse transcription[edit]
Reverse transcriptase creates double-stranded DNA from an RNA template.
In virus species with reverse transcriptase lacking DNA-dependent DNA polymerase activity, creation of double-stranded DNA can possibly be done by host-encoded DNA polymerase δ, mistaking the viral DNA-RNA for a primer and synthesizing a double-stranded DNA by similar mechanism as in primer removal, where the newly synthesized DNA displaces the original RNA template.
The process of reverse transcription is extremely error-prone, and it is during this step that mutations may occur. Such mutations may cause drug resistance.
Retroviral reverse transcription[edit]
Retroviruses, also referred to as class VI ssRNA-RT viruses, are RNA reverse-transcribing viruses with a DNA intermediate. Their genomes consist of two molecules of positive-sense single-stranded RNA with a 5' cap and 3' polyadenylated tail. Examples of retroviruses include the human immunodeficiency virus (HIV) and the human T-lymphotropic virus (HTLV). Creation of double-stranded DNA occurs in the cytosol[7] as a series of these steps:
Lysyl tRNA acts as a primer and hybridizes to a complementary part of the virus RNA genome called the primer binding site or PBS.
Reverse transcriptase then adds DNA nucleotides onto the 3' end of the primer, synthesizing DNA complementary to the U5 (non-coding region) and R region (a direct repeat found at both ends of the RNA molecule) of the viral RNA.
A domain on the reverse transcriptase enzyme called RNAse H degrades the U5 and R regions on the 5’ end of the RNA.
The primer then "jumps" to the 3’ end of the viral genome, and the newly synthesised DNA strands hybridizes to the complementary R region on the RNA.
The complementary DNA (cDNA) added in (2) is further extended, and then the majority of viral RNA is degraded by RNAse H, leaving only the PP sequence.
Synthesis of the second DNA strand begins, using the remaining fragment of viral RNA as a primer.
There is then another "jump" where the PBS from the second strand hybridizes with the complementary PBS on the first strand.
Both strands are extended to form a complete double-stranded DNA copy of the original viral RNA genome, which can then be incorporated into the host's genome by the enzyme integrase.
Creation of double-stranded DNA also involves strand transfer, in which there is a translocation of short DNA product from initial RNA-dependent DNA synthesis to acceptor template regions at the other end of the genome, which are later reached and processed by the reverse transcriptase for its DNA-dependent DNA activity.[8]
Retroviral RNA is arranged in 5’ terminus to 3’ terminus. The site where the primer is annealed to viral RNA is called the primer-binding site (PBS). The RNA 5’end to the PBS site is called U5, and the RNA 3’ end to the PBS is called the leader. The tRNA primer is unwound between 14 and 22 nucleotides and forms a base-paired duplex with the viral RNA at PBS. The fact that the PBS is located near the 5’ terminus of viral RNA is unusual because reverse transcriptase synthesize DNA from 3’ end of the primer in the 5’ to 3’ direction (with respect to the RNA template). Therefore, the primer and reverse transcriptase must be relocated to 3’ end of viral RNA. In order to accomplish this reposition, multiple steps and various enzymes including DNA polymerase, ribonuclease H(RNase H) and polynucleotide unwinding are needed.[9][10]

The HIV reverse transcriptase also has ribonuclease activity that degrades the viral RNA during the synthesis of cDNA, as well as DNA-dependent DNA polymerase activity that copies the sense cDNA strand into an antisense DNA to form a double-stranded viral DNA intermediate (vDNA).[11]
In eukaryotes[edit]
Self-replicating stretches of eukaryotic genomes known as retrotransposons utilize reverse transcriptase to move from one position in the genome to another via an RNA intermediate. They are found abundantly in the genomes of plants and animals. Telomerase is another reverse transcriptase found in many eukaryotes, including humans, which carries its own RNA template; this RNA is used as a template for DNA replication.[12]
In prokaryotes[edit]
Initial reports of reverse transcriptase in prokaryotes came as far back as 1971 (Beljanski et al., 1971a, 1972). These have since been broadly described as part of bacterial Retrons, distinct sequences that code for reverse transcriptase, and are used in the synthesis of msDNA. In order to initiate synthesis of DNA, a primer is needed. In bacteria, the primer is synthesized during replication.[13]
Evolutionary role[edit]
Valerian Dolja of Oregon State argues that viruses, due to their diversity, have played an evolutionary role in the development of cellular life, with reverse transcriptase playing a central role.[14]
Structure[edit]
Reverse transcriptase enzymes include an RNA-dependent DNA polymerase and a DNA-dependent DNA polymerase, which work together to perform reverse transcription. In addition to the transcription function, retroviral reverse transcriptases have a domain belonging to the RNase H family, which is vital to their replication.
Replication fidelity[edit]
There are three different replication systems during the life cycle of a retrovirus. First of all, the reverse transcriptase synthesizes viral DNA from viral RNA, and then from newly made complementary DNA strand. The second replication process occurs when host cellular DNA polymerase replicates the integrated viral DNA. Lastly, RNA polymerase II transcribes the proviral DNA into RNA, which will be packed into virions. Therefore, mutation can occur during one or all of these replication steps.[15]
Reverse transcriptase has a high error rate when transcribing RNA into DNA since, unlike most other DNA polymerases, it has no proofreading ability. This high error rate allows mutations to accumulate at an accelerated rate relative to proofread forms of replication. The commercially available reverse transcriptases produced by Promega are quoted by their manuals as having error rates in the range of 1 in 17,000 bases for AMV and 1 in 30,000 bases for M-MLV.[16]
Other than creating single-nucleotide polymorphisms, reverse transcriptases have also been shown to be involved in processes such as transcript fusions, exon shuffling and creating artificial antisense transcripts.[17][18] It has been speculated that this template switching activity of reverse transcriptase, which can be demonstrated completely in vivo, may have been one of the causes for finding several thousand unannotated transcripts in the genomes of model organisms.[19]
Applications[edit]
The molecular structure of zidovudine (AZT), a drug used to inhibit HIV reverse transcriptase
Antiviral drugs[edit]
Further information: Reverse-transcriptase inhibitor
As HIV uses reverse transcriptase to copy its genetic material and generate new viruses (part of a retrovirus proliferation circle), specific drugs have been designed to disrupt the process and thereby suppress its growth. Collectively, these drugs are known as reverse-transcriptase inhibitors and include the nucleoside and nucleotide analogues zidovudine (trade name Retrovir), lamivudine (Epivir) and tenofovir (Viread), as well as non-nucleoside inhibitors, such as nevirapine (Viramune).
Molecular biology[edit]
Further information: Reverse transcription polymerase chain reaction
Reverse transcriptase is commonly used in research to apply the polymerase chain reaction technique to RNA in a technique called reverse transcription polymerase chain reaction (RT-PCR). The classical PCR technique can be applied only to DNA strands, but, with the help of reverse transcriptase, RNA can be transcribed into DNA, thus making PCR analysis of RNA molecules possible. Reverse transcriptase is used also to create cDNA libraries from mRNA. The commercial availability of reverse transcriptase greatly improved knowledge in the area of molecular biology, as, along with other enzymes, it allowed scientists to clone, sequence, and characterise RNA.
Reverse transcriptase has also been employed in insulin production. By inserting eukaryotic mRNA for insulin production along with reverse transcriptase into bacteria, the mRNA could be inserted into the prokaryote's genome. Large amounts of insulin can then be created, sidestepping the need to harvest pig pancreas and other such traditional sources. Directly inserting eukaryotic DNA into bacteria would not work because it carries introns, so would not translate successfully using the bacterial ribosomes. Processing in the eukaryotic cell during mRNA production removes these introns to provide a suitable template. Reverse transcriptase converted this edited RNA back into DNA so it could be incorporated in the genome.
See also[edit]
Molecular and cellular biology portal
Viruses portal
cDNA library
DNA polymerase
msDNA
Reverse transcribing virus
RNA polymerase
Telomerase
Retrotransposon marker
References[edit]
Jump up ^ PDB: 3KLF; Tu X, Das K, Han Q, Bauman JD, Clark AD, Hou X, Frenkel YV, Gaffney BL, Jones RA, Boyer PL, Hughes SH, Sarafianos SG, Arnold E (September 2010). "Structural basis of HIV-1 resistance to AZT by excision". Nat. Struct. Mol. Biol. 17 (10): 1202–9. doi:10.1038/nsmb.1908. PMC 2987654  . PMID 20852643.
Jump up ^ Ferris, AL; Hizi, A; Showalter, SD; Pichuantes, S; Babe, L; Craik, CS; Hughes, SH (April 1990). "Immunologic and proteolytic analysis of HIV-1 reverse transcriptase structure" (PDF). Virology. 175 (2): 456–64. doi:10.1016/0042-6822(90)90430-y. PMID 1691562.
^ Jump up to: a b Konishi A, Yasukawa K, Inouye K (2012). "Improving the thermal stability of avian myeloblastosis virus reverse transcriptase α-subunit by site-directed mutagenesis" (PDF). Biotechnol. Lett. 34 (7): 1209–15. doi:10.1007/s10529-012-0904-9. PMID 22426840.
Jump up ^ Temin HM, Mizutani S (June 1970). "RNA-dependent DNA polymerase in virions of Rous sarcoma virus". Nature. 226 (5252): 1211–3. doi:10.1038/2261211a0. PMID 4316301.
Jump up ^ Baltimore D. (June 1970). "RNA-dependent DNA polymerase in virions of RNA tumour viruses". Nature. 226 (5252): 1209–11. doi:10.1038/2261209a0. PMID 4316300.
Jump up ^ "Central dogma reversed". Nature. 226 (5252): 1198–9. June 1970. doi:10.1038/2261198a0. PMID 5422595.
Jump up ^ Bio-Medicine.org - Retrovirus Retrieved on 17 Feb, 2009
Jump up ^ Telesnitsky A, Goff SP (1993). "Strong-stop strand transfer during reverse transcription". In Skalka MA, Goff SP. Reverse transcriptase (1st ed.). New York: Cold Spring Harbor. p. 49. ISBN 0-87969-382-7.
Jump up ^ Bernstein A, Weiss R, Tooze J (1985). "RNA tumor viruses". Molecular Biology of Tumor Viruses (2nd ed.). Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory.
Jump up ^ Moelling, Karin; Broecker, Felix (2015). "The reverse transcriptase-RNase H: from viruses to antiviral defense". Annals of the New York Academy of Sciences. 1341 (1): 126–135. doi:10.1111/nyas.12668. ISSN 0077-8923.
Jump up ^ Doc Kaiser's Microbiology Home Page > IV. VIRUSES > F. ANIMAL VIRUS LIFE CYCLES > 3. The Life Cycle of HIV Archived 2010-07-26 at the Wayback Machine. Community College of Baltimore County. Updated: Jan 2008.
Jump up ^ Krieger M, Scott MP, Matsudaira PT, Lodish HF, Darnell JE, Zipursky L, Kaiser C, Berk A (2004). Molecular cell biology. New York: W.H. Freeman and CO. ISBN 0-7167-4366-3.
Jump up ^ Hurwitz J, Leis JP (January 1972). "RNA-dependent DNA polymerase activity of RNA tumor viruses. I. Directing influence of DNA in the reaction". J. Virol. 9 (1): 116–29. PMC 356270  . PMID 4333538.
Jump up ^ Arnold, Carrie (17 July 2014). "Could Giant Viruses Be the Origin of Life on Earth?". news.nationalgeographic.com. Retrieved 29 May 2016.
Jump up ^ Bbenek K, Kunkel AT (1993). "The fidelity of retroviral reverse transcriptases". In Skalka MA, Goff PS. Reverse transcriptase. New York: Cold Spring Harbor Laboratory Press. p. 85. ISBN 0-87969-382-7.
Jump up ^ Promega kit instruction manual (1999) Archived 2006-11-21 at the Wayback Machine.
Jump up ^ Houseley J, Tollervey D (2010). "Apparent non-canonical trans-splicing is generated by reverse transcriptase in vitro". PLoS ONE. 5 (8): e12271. doi:10.1371/journal.pone.0012271. PMC 2923612  . PMID 20805885.
Jump up ^ Zeng XC, Wang SX (June 2002). "Evidence that BmTXK beta-BmKCT cDNA from Chinese scorpion Buthus martensii Karsch is an artifact generated in the reverse transcription process". FEBS Lett. 520 (1–3): 183–4; author reply 185. doi:10.1016/S0014-5793(02)02812-0. PMID 12044895.
Jump up ^ van Bakel H, Nislow C, Blencowe BJ, Hughes TR (2011). "Response to "The Reality of Pervasive Transcription"". PLoS Biology. 9 (7): e1001102. doi:10.1371/journal.pbio.1001102.
External links[edit]
RNA Transcriptase at the US National Library of Medicine Medical Subject Headings (MeSH)
animation of reverse transcriptase action and three reverse transcriptase inhibitors
Molecule of the month (September 2002) at the RCSB PDB
HIV Replication 3D Medical Animation. (Nov 2008). Video by Boehringer Ingelheim.
Goodsell DS. "Molecule of the Month: Reverse Transcriptase (Sep 2002)". Research Collaboratory for Structural Bioinformatics (RCSB) Protein Data Bank (PDB). Retrieved 2013-01-13.
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Marriage Act 1961 (Australia)
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This article may require copy editing for grammar, style, cohesion, tone, or spelling. You can assist by editing it. (July 2017) (Learn how and when to remove this template message)
Marriage Act 1961
Parliament of Australia
An Act relating to Marriage
Citation
No. 12, 1961
Date of Royal Assent
6 May 1961
Status: Current legislation
In Australia, the Marriage Act 1961 is the current Act that regulates marriage law in Australia.
The Act was passed by the Australian Parliament and has been amended on numerous occasions and applies uniformly throughout Australia (including its external territories); and any law made by a State or Territory inconsistent with the Act is invalid. The Act is made pursuant to power granted to the federal parliament under s.51(xxi) of the Australian Constitution. The Act recognises only marriages of two people and does not recognise any other forms of union, including traditional Aboriginal unions.[1] An amendment to the Act to legalise same-sex marriage passed into law on 8 December 2017. The Family Law Act 1975 treats de facto relationships and polygamous marriages[2] as marriages for the purpose of recognising the rights of parties at a breakup. Since 2009, the Family Law Act 2009 has also recognised the property rights of each partner of de facto relationships on separation.
Contents
[hide]
1 Marriageable age
2 Void marriages
3 Solemnisation of marriages in Australia
3.1 Authorised celebrants
3.1.1 Religious ministers
3.1.2 Registry office marriages
3.1.3 Civil celebrants
4 Recognition of foreign marriages
5 Other sections
6 Marriage education
7 Amendments to the Marriage Act
7.1 Marriage Amendment Act 2004
7.2 Marriage Amendment (Definition and Religious Freedoms) Act 2017
8 Same-sex marriage in the ACT
9 See also
10 References
11 External sources
Marriageable age[edit]
Part II (s.10-21) deals with the marriageable age and the marriage of minors. In the original 1961 Act, marriageable age was set at 16 for females and 18 for males. The marriageable age was equalised in 1991 by the Sex Discrimination Amendment Act 1991[3] which raised the marriageable age of females to 18.
The marriage of a person aged 16 or 17 to another aged over 18 is permitted in 'unusual and exceptional circumstances’, which requires the consent of the younger person's parents and authorisation by a court. Prior to the 1991 changes, the 'unusual and exceptional circumstances' procedures applied to a girl aged 14 or 15 (wanting to marry a male aged 18 or above) or a male aged 16 or 17 (wanting to marry a female aged 16 or above).[4] For many years, courts have refused to accept a minor's pregnancy as a pressing consideration in deciding whether to allow an early marriage.[5]
Void marriages[edit]
Part III entitled ‘void marriages’ establishes the circumstances in which a marriage is void. To preserve the validity of past marriages, this part is divided into years based on when amendments to this Act were introduced.
A purported marriage is void if:
either party is already married (bigamy, polygamy).
the parties are in a prohibited relationship: direct descendants or siblings, including adopted (by law) relationships.
the marriage was not solemnised by an authorised celebrant (as in Part IV, Division 2).
there is no consent, for example due to duress, fraud, mistake as to identity, mistake as to nature of ceremony, mental incapacity, or below marriageable age in Part II.
Solemnisation of marriages in Australia[edit]
Part IV entitled ‘Solemnisation of Marriages in Australia’ deals with who is authorised to be a wedding celebrant, and the procedures to be followed. It also contains a division on marriages by foreign diplomatic or consular officers.
Authorised celebrants[edit]
Division 1 deals with authorised celebrants. Under the current Act three types of celebrants are allowed: ministers of religion, State and Territory officers, and (civil) marriage celebrants.
Religious ministers[edit]
Under Subdivision A, a register is kept of ministers of religion (s.27) of ‘recognised’ denominations (s26). The only requirements for registration is that the person is a minister of religion[6] who is nominated by their denomination and is resident in Australia and over 21 years (s29). A minister will be registered (s30) unless the registrar refuses registration because there are sufficient ministers of that denomination, the minister is ‘not a fit and proper person’, or will not devote sufficient time to the functions of a minister of religion (s31). In general, the act establishes a broad scheme which recognises a religious wedding ceremony that is conducted by a registered minister.
Ministers of religion are not bound to solemnise any marriage. Nothing in Part IV of the Marriage Act imposes an obligation on an authorised celebrant, being a minister of religion, to solemnise any marriage (s47).
Registry office marriages[edit]
Subdivision B (s.39) preserves the power of ‘state and territory officers’, allowing people who register marriages (under a state law) to also solemnise marriages (i.e. registry marriages).
Civil celebrants[edit]
Subdivision C deals with ‘marriage celebrants’, or the authorisation of people to conduct civil ceremonies. Section 39B allows the register to be kept and sections 39D-E are procedural and seek to set up processes to control the number of celebrants.
This section was introduced by the Marriage Amendment Act 2002, after an Attorney-General inquiry into the Civil Celebrants Program. Prior to the passage of this amendment the authorisation of celebrants was entirely contained in s39, which had a s39(2) allowing the recognition of other ‘fit and proper persons’ as civil marriage celebrants, religious celebrants outside a recognised denomination, and celebrants with special community needs.
The original 1961 Act therefore allowed civil ceremonies, and the first civil celebrants were authorised in 1973. By the time the amendments were introduced civil celebrants performed over 50% of marriages. The changes therefore provide legislative recognition to civil celebrants, and prescribe a regime beyond being ‘fit and proper’ in order to control the quality and number of celebrants.
Section 39C now lists a number of requirements to be registered as civil celebrant, in addition to being over 18 and ‘fit and proper’. The register will take into account: knowledge of the law, a commitment to advising about relationship counselling, good community standing, criminal record, the existence of a conflict of interest or benefit to business, and ‘any other matter’.
Section 39G imposes ‘obligations’ on civil celebrants. These include professional development and an adherence to a code of practice.
Sections 39H, I, and J set up a review of celebrants and a disciplinary system.
Significantly, Subdivision C deals only with marriage celebrants (civil or not a recognised religion), not with ministers of religion which are governed by Subdivision A. As a result, ministers of religion are not necessarily subject to the same obligations or code of practice.
Recognition of foreign marriages[edit]
Part VA deals with recognition of foreign marriages.
This division reflects the Act's tendency to seek to uphold the validity of marriages. Marriages will be recognised if they were valid in the country where they were performed if the marriage would be legal under Australian law. The foreign marriage certificate is proof of marriage and marriages need not be registered.
As a marriage must be legal under Australian law, a foreign marriage will not be recognised if a person was already married (or the overseas divorce is not recognised in Australia), a person was under 18 (subject to some exceptions), the persons were siblings or parent/child, or there was duress or fraud.
Other sections[edit]
Marriages by Foreign Diplomatic or Consular Officers (Division 3 of Part IV): there are currently no Australian diplomatic or consular officers appointed to solemnise marriages overseas under Australian law.
Marriages of Members of the Defence Force Overseas: Part V of the act deals with marriages of members of the Defence Force overseas.
Legitimation of children (Part VI) The Act legitimises children if their parents marry, including some recognised foreign marriages, or result from a void marriages.
Offences (Part VII): e.g. bigamy, marrying a person below marriageable age (child marriages), a celebrant solemnising a marriage when believe legal impediment etc.
Miscellaneous provisions in Part IX – interpreters, publication of lists of celebrants, etc.
Section 111A removed the ability to seek to recover damages for breach of contract where a promise to marry (an engagement) did not lead to marriage.
Marriage education[edit]
Part IA authorises the government to make grants to approved organisations for marriage counselling.
Amendments to the Marriage Act[edit]
Two amendments of note to the Act have been made with respect to the legal definition of "marriage" in Australia, both of which relate to same-sex marriage.
Marriage Amendment Act 2004[edit]
Before 2004, there was no definition of marriage in the 1961 Act, and instead the common law definition used in the English case Hyde v Hyde (1866) was considered supreme.[7] Though Sect 46(1) of the Act required celebrants to explain the legal nature of marriage in Australia to a couple as "the union of a man and a woman to the exclusion of all others, voluntarily entered into for life", these words were descriptive or explanatory, rather than outlining what constituted a legally valid marriage in Australia.[8]
On 27 May 2004 the then federal Attorney-General Philip Ruddock introduced the Marriage Amendment Bill 2004 to incorporate a definition of marriage into the Marriage Act 1961 and to outlaw the recognition of same-sex marriages lawfully entered into in foreign jurisdictions.[9][10] In June 2004, the bill passed the House of Representatives. On 12 August 2004, the amendment passed the Parliament. The bill subsequently received royal assent, becoming the Marriage Amendment Act 2004.[11][12]
The amendment incorporated a definition of marriage into section 5 of the Act, known was the Interpretation section:
marriage means the union of a man and a woman to the exclusion of all others, voluntarily entered into for life.
and inserted a new section:
88EA Certain unions are not marriages
A union solemnised in a foreign country between:
(a) a man and another man; or
(b) a woman and another woman;
must not be recognised as a marriage in Australia.[13]
The amendment was argued by Ruddock and Liberal MPs to be necessary to protect the institution of marriage, and ensure that the definition would be beyond legal challenge through the application of common law.[14] Several years later, then-Prime Minister John Howard admitted that the government was motivated by the prospect of overseas same-sex marriages being recognised under Australian law via the judiciary.[15] Labor Party shadow Attorney-General Nicola Roxon said that the Labor would not oppose the amendment, arguing that the amendment did not affect the legal situation of same-sex relationships, merely putting into statute law what was already common law. Likewise minor parties Family First and the Christian Democrats parties supported the bill, as did the junior party in the Coalition government, the National Party.
Despite having the support of the major parties, the bill was bitterly contested by sections of the community, human rights groups and some minor political parties. The Australian Greens opposed the bill, calling it the "Marriage Discrimination Act". The Australian Democrats also opposed the bill. Democrat Senator Andrew Bartlett stated that the legislation devalues his marriage, and Greens Senator Bob Brown referred to John Howard and the legislation as "hateful".[16][17][18]
Not all of Labor was in support of the bill. During the bill's second reading, Labor MP Anthony Albanese said, "what has caused offence is why the government has rushed in this legislation in what is possibly the last fortnight of parliamentary sittings. This bill is a result of 30 bigoted backbenchers who want to press buttons out there in the community."[19]
Marriage Amendment (Definition and Religious Freedoms) Act 2017[edit]
Main article: Marriage Amendment (Definition and Religious Freedoms) Act 2017
See also: Australian Marriage Law Postal Survey
Ahead of both the 2007 and 2010 federal elections, the Labor Party re-asserted its official opposition to amending the Act to legalise same-sex marriage, though by 2011 a clear majority of the party at the national conference succeeded in changing party policy in favour of the practice.[20] Prime Minister Julia Gillard (opposed to same-sex marriage at the time) successfully moved for a Labor Party MPs to be granted a conscience vote on same-sex marriage legislation.[21] This, along with the Coalition's uniform opposition to same-sex marriage whilst in opposition prevented two bills which would have legalised same-sex marriage in Australia from passing the House of Representatives and Senate in September 2012.[22][23]
The Abbott Government (2013-15) initially opposed same-sex marriage, but in August 2015 resolved to put the matter to the people at a plebiscite after the 2016 federal election. This policy was retained by the Turnbull Government (2015-present), though due to the refusal of the Senate to support the legislation to establish a plebiscite, the government conducted a voluntary postal survey on the matter from September to November 2017. The survey returned 61.6% "Yes" vote in favour of same-sex marriage. The government subsequently committed to facilitating the passage of a private member's bill to amend the Act, and legalise same-sex marriage, by the end of 2017.[24]
The bill in question, the Marriage Amendment (Definition and Religious Freedoms) Bill 2017, was introduced by Liberal Party Senator Dean Smith on 15 November 2017. The bill amends the definition of "marriage" in the Act, omitting the words "man and a woman" and replacing it with the gender-neutral statement "2 people".[25][26] The bill passed the Senate by 43 votes to 12 on 29 November 2017 and passed the House of Representatives on 7 December 2017, with only four votes against.[27][28] It was given royal assent by the Governor General, Sir Peter Cosgrove, on 8 December 2017.[29]
The Act had the effect of amending the definition of marriage in Section 5 of the Marriage Act:
marriage means the union of 2 people to the exclusion of all others, voluntarily entered into for life.
It also repealed Section 88EA, which banned the recognition of overseas same-sex marriages. Consequently, when the Act went into effect on 9 December 2017, such couples became automatically recognised as married under the law.[29][30]
The original Act and the amendment also applies to Australia’s external territories.
Same-sex marriage in the ACT[edit]
In October 2013, same-sex marriage was legalised in the Australian Capital Territory (ACT). The ACT legislation was overturned by the High Court for being inconsistent with the Marriage Act.[31] This was due to the definition of the term 'marriage' in the Marriage Act, which at that time excluded all types of marriage other than that between one man and one woman.[32]
See also[edit]
Celebrant (Australia)
Marriage Act
Marriage in Australia
Same-sex marriage in Australia
References[edit]
Jump up ^ Australian Government, Law Reform Commission - Aboriginal Traditional Marriage: Areas for Recognition
Jump up ^ Family Law Act 1975 - S.6 Polygamous marriages
Jump up ^ "ComLaw Acts - Attachment - Sex Discrimination Amendment Act 1991". Scaleplus.law.gov.au. Archived from the original on 16 February 2012.
Jump up ^ http://www.comlaw.gov.au/Details/C2004C05245
Jump up ^ "Lawstuff Australia - Know Your Rights - Topics - Marriage".
Jump up ^ and is nominated by a proclaimed 'recognised denomination' as defined under s26 of the Marriage Act 1961. The term 'minister of religion' need not correspond to the actual office or title of the celebrant.
Jump up ^ Hyde v. Hyde and Woodmansee {L.R.} 1 P. & D. 130.
Jump up ^ Neilsen, Mary Anne (10 February 2012). "Same-sex marriage". Background Notes 2011-2012. Parliamentary Library (Australia). Retrieved 27 December 2016.
Jump up ^ http://www.aph.gov.au/Parliamentary_Business/Bills_Legislation/bd/bd0405/05bd005
Jump up ^ http://parlinfoweb.aph.gov.au/piweb/translatewipilink.ASPX?Folder=HANSARDR&Criteria=DOC_DATE:2004-05-27;SEQ_NUM:42;
Jump up ^ Text of Marriage Amendment Act 2004 (pdf)
Jump up ^ [1] Archived 29 October 2009 at the Wayback Machine.
Jump up ^ "Marriage Amendment Act 2004". Retrieved 9 August 2017.
Jump up ^ "Archived copy". Archived from the original on 24 May 2011. Retrieved 2010-06-01.
Jump up ^ "John Howard defends Malcolm Turnbull on same-sex plebiscite". The Australian. 8 August 2017. (Subscription required (help)). John Howard: "What we didn’t want to happen in 2004 was for the courts to start adjudicating on the definition of marriage because that was a real threat in 2004 because some people who had contracted same sex marriages in another country had the capacity to bring their issues before courts in Australia".
Jump up ^ http://parlinfoweb.aph.gov.au/piweb/translatewipilink.ASPX?Folder=HANSARDS&Criteria=DOC_DATE:2004-08-12;SEQ_NUM:324;
Jump up ^ "Coalition, Labor pass same-sex marriage ban". ABC News Online. 2004-08-13.
Jump up ^ Wright, Tim (31 July 2009). "Same-sex couples still waiting at the altar for a basic right". The Sydney Morning Herald. Retrieved 7 September 2017.
Jump up ^ Albanese, Anthony (2004-06-16). "Marriage Legislation Amendment Bill 2004: Second Reading". Anthony Albanese MP. Archived from the original on 5 June 2008. Retrieved 2008-05-26.
Jump up ^ "Labor decides on conscience vote for gay marriage". ABC News. Australian Broadcasting Corporation. 3 December 2011. Retrieved 4 December 2016.
Jump up ^ "Labor backs same-sex marriage". News Corporation.
Jump up ^ "Lower House votes down same-sex marriage bill". ABC News.
Jump up ^ "Australian Senate votes down same-sex marriage bill". ABC News.
Jump up ^ "Australia says yes to same-sex marriage in historic postal survey". The Guardian. 15 November 2017.
Jump up ^ "Explanatory Memorandum: Marriage Amendment (Definition and Religious Freedoms) Bill 2017". Parliament of Australia. 15 November 2017.
Jump up ^ "Dean Smith introduces same-sex marriage bill to parliament". The Guardian. 16 November 2017.
Jump up ^ "Same-sex marriage bill passes Senate with day to spare before House of Representatives resumes". ABC News. 29 November 2017.
Jump up ^ "Same-sex marriage bill passes House of Representatives after hundreds of hours of debate". ABC News. 7 December 2017.
^ Jump up to: a b "Same-sex marriage gets the Governor-General's big tick". ABC News. 8 December 2017.
Jump up ^ "Marriage Amendment (Definition and Religious Freedoms) Act 2017". Federal Register of Legislation. 9 December 2017.
Jump up ^ "The Commonwealth v Australian Capital Territory [2013] HCA 55".
Jump up ^ "MARRIAGE ACT 1961 - SECT 5 Interpretation". www.austlii.edu.au. Retrieved 2016-03-09.
External sources[edit]
Marriage Act 1961 on Austlii
Proposal to Reform the Civil Marriage Celebrants Programme
Discussion Paper on Civil Celebrants Programme (October 1997)
Bills Digest on the Marriage Amendment Act 2002
Recognition of Foreign Marriages
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Extreme programming
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Planning and feedback loops in extreme programming.
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Extreme programming (XP) is a software development methodology which is intended to improve software quality and responsiveness to changing customer requirements. As a type of agile software development,[1][2][3] it advocates frequent "releases" in short development cycles, which is intended to improve productivity and introduce checkpoints at which new customer requirements can be adopted.
Other elements of extreme programming include: programming in pairs or doing extensive code review, unit testing of all code, avoiding programming of features until they are actually needed, a flat management structure, code simplicity and clarity, expecting changes in the customer's requirements as time passes and the problem is better understood, and frequent communication with the customer and among programmers.[2][3][4] The methodology takes its name from the idea that the beneficial elements of traditional software engineering practices are taken to "extreme" levels. As an example, code reviews are considered a beneficial practice; taken to the extreme, code can be reviewed continuously, i.e. the practice of pair programming.
Contents
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1 History
1.1 Origins
1.2 Current state
2 Concept
2.1 Goals
2.2 Activities
2.2.1 Coding
2.2.2 Testing
2.2.3 Listening
2.2.4 Designing
2.3 Values
2.3.1 Communication
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2.3.3 Feedback
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2.4 Rules
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2.5.1 Feedback
2.5.2 Assuming simplicity
2.5.3 Embracing change
3 Practices
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3.2 Continuous process
3.3 Shared understanding
3.4 Programmer welfare
3.5 Coding
3.6 Testing
4 Controversial aspects
4.1 Scalability
4.2 Severability and responses
5 Criticism
6 See also
7 References
8 Further reading
9 Further reading
10 External links
History[edit]
Extreme programming was created by Kent Beck during his work on the Chrysler Comprehensive Compensation System (C3) payroll project.[5] Beck became the C3 project leader in March 1996 and began to refine the development methodology used in the project and wrote a book on the methodology (in October 1999, Extreme Programming Explained was published).[5] Chrysler cancelled the C3 project in February 2000, after seven years, when the company was acquired by Daimler-Benz.[6]
Many of extreme programming practices have been around for some time; the methodology takes "best practices" to extreme levels. For example, the "practice of test-first development, planning and writing tests before each micro-increment" was used as early as NASA's Project Mercury, in the early 1960s (Larman 2003). To shorten the total development time, some formal test documents (such as for acceptance testing) have been developed in parallel (or shortly before) the software is ready for testing. A NASA independent test group can write the test procedures, based on formal requirements and logical limits, before the software has been written and integrated with the hardware. In XP, this concept is taken to the extreme level by writing automated tests (perhaps inside of software modules) which validate the operation of even small sections of software coding, rather than only testing the larger features.
Origins[edit]
Software development in the 1990s was shaped by two major influences: internally, object-oriented programming replaced procedural programming as the programming paradigm favored by some in the industry; externally, the rise of the Internet and the dot-com boom emphasized speed-to-market and company growth as competitive business factors. Rapidly changing requirements demanded shorter product life-cycles, and were often incompatible with traditional methods of software development.
The Chrysler Comprehensive Compensation System (C3) was started in order to determine the best way to use object technologies, using the payroll systems at Chrysler as the object of research, with Smalltalk as the language and GemStone as the data access layer. They brought in Kent Beck,[5] a prominent Smalltalk practitioner, to do performance tuning on the system, but his role expanded as he noted several problems they were having with their development process. He took this opportunity to propose and implement some changes in their practices based on his work with his frequent collaborator, Ward Cunningham. Beck describes the early conception of the methods:[7]
The first time I was asked to lead a team, I asked them to do a little bit of the things I thought were sensible, like testing and reviews. The second time there was a lot more on the line. I thought, "Damn the torpedoes, at least this will make a good article," [and] asked the team to crank up all the knobs to 10 on the things I thought were essential and leave out everything else.
Beck invited Ron Jeffries to the project to help develop and refine these methods. Jeffries thereafter acted as a coach to instill the practices as habits in the C3 team.
Information about the principles and practices behind XP was disseminated to the wider world through discussions on the original wiki, Cunningham's WikiWikiWeb. Various contributors discussed and expanded upon the ideas, and some spin-off methodologies resulted (see agile software development). Also, XP concepts have been explained, for several years, using a hypertext system map on the XP website at "http://www.extremeprogramming.org" circa 1999.
Beck edited a series of books on XP, beginning with his own Extreme Programming Explained (1999, ISBN 0-201-61641-6), spreading his ideas to a much larger audience. Authors in the series went through various aspects attending XP and its practices. The series included a book that was critical of the practices.
Current state[edit]
XP generated significant interest among software communities in the late 1990s and early 2000s, seeing adoption in a number of environments radically different from its origins.
The high discipline required by the original practices often went by the wayside, causing some of these practices, such as those thought too rigid, to be deprecated or reduced, or even left unfinished, on individual sites. For example, the practice of end-of-day integration tests for a particular project could be changed to an end-of-week schedule, or simply reduced to mutually agreed dates. Such a more relaxed schedule could avoid people feeling rushed to generate artificial stubs just to pass the end-of-day testing. A less-rigid schedule allows, instead, for some complex features to be more fully developed over a several-day period.
Meanwhile, other agile development practices have not stood still, and XP is still evolving, assimilating more lessons from experiences in the field, to use other practices. In the second edition of Extreme Programming Explained (November 2004), five years after the first edition, Beck added more values and practices and differentiated between primary and corollary practices.
Concept[edit]
Goals[edit]
Extreme Programming Explained describes extreme programming as a software-development discipline that organizes people to produce higher-quality software more productively.
XP attempts to reduce the cost of changes in requirements by having multiple short development cycles, rather than a long one. In this doctrine, changes are a natural, inescapable and desirable aspect of software-development projects, and should be planned for, instead of attempting to define a stable set of requirements.
Extreme programming also introduces a number of basic values, principles and practices on top of the agile programming framework.
Activities[edit]
XP describes four basic activities that are performed within the software development process: coding, testing, listening, and designing. Each of those activities is described below.
Coding[edit]
The advocates of XP argue that the only truly important product of the system development process is code – software instructions that a computer can interpret. Without code, there is no working product.
Coding can also be used to figure out the most suitable solution. Coding can also help to communicate thoughts about programming problems. A programmer dealing with a complex programming problem, or finding it hard to explain the solution to fellow programmers, might code it in a simplified manner and use the code to demonstrate what he or she means. Code, say the proponents of this position, is always clear and concise and cannot be interpreted in more than one way. Other programmers can give feedback on this code by also coding their thoughts.
Testing[edit]
Main article: Test-driven development
Extreme programming's approach is that if a little testing can eliminate a few flaws, a lot of testing can eliminate many more flaws.
Unit tests determine whether a given feature works as intended. Programmers write as many automated tests as they can think of that might "break" the code; if all tests run successfully, then the coding is complete. Every piece of code that is written is tested before moving on to the next feature.
Acceptance tests verify that the requirements as understood by the programmers satisfy the customer's actual requirements.
System-wide integration testing was encouraged, initially, as a daily end-of-day activity, for early detection of incompatible interfaces, to reconnect before the separate sections diverged widely from coherent functionality. However, system-wide integration testing has been reduced, to weekly, or less often, depending on the stability of the overall interfaces in the system.[citation needed]
Listening[edit]
Programmers must listen to what the customers need the system to do, what "business logic" is needed. They must understand these needs well enough to give the customer feedback about the technical aspects of how the problem might be solved, or cannot be solved. Communication between the customer and programmer is further addressed in the planning game.
Designing[edit]
From the point of view of simplicity, of course one could say that system development doesn't need more than coding, testing and listening. If those activities are performed well, the result should always be a system that works. In practice, this will not work. One can come a long way without designing but at a given time one will get stuck. The system becomes too complex and the dependencies within the system cease to be clear. One can avoid this by creating a design structure that organizes the logic in the system. Good design will avoid lots of dependencies within a system; this means that changing one part of the system will not affect other parts of the system.[citation needed]
Values[edit]
Extreme programming initially recognized four values in 1999: communication, simplicity, feedback, and courage. A new value, respect, was added in the second edition of Extreme Programming Explained. Those five values are described below.
Communication[edit]
Building software systems requires communicating system requirements to the developers of the system. In formal software development methodologies, this task is accomplished through documentation. Extreme programming techniques can be viewed as methods for rapidly building and disseminating institutional knowledge among members of a development team. The goal is to give all developers a shared view of the system which matches the view held by the users of the system. To this end, extreme programming favors simple designs, common metaphors, collaboration of users and programmers, frequent verbal communication, and feedback.
Simplicity[edit]
Extreme programming encourages starting with the simplest solution. Extra functionality can then be added later. The difference between this approach and more conventional system development methods is the focus on designing and coding for the needs of today instead of those of tomorrow, next week, or next month. This is sometimes summed up as the "You aren't gonna need it" (YAGNI) approach.[8] Proponents of XP acknowledge the disadvantage that this can sometimes entail more effort tomorrow to change the system; their claim is that this is more than compensated for by the advantage of not investing in possible future requirements that might change before they become relevant. Coding and designing for uncertain future requirements implies the risk of spending resources on something that might not be needed, while perhaps delaying crucial features. Related to the "communication" value, simplicity in design and coding should improve the quality of communication. A simple design with very simple code could be easily understood by most programmers in the team.
Feedback[edit]
Within extreme programming, feedback relates to different dimensions of the system development:
Feedback from the system: by writing unit tests,[5] or running periodic integration tests, the programmers have direct feedback from the state of the system after implementing changes.
Feedback from the customer: The functional tests (aka acceptance tests) are written by the customer and the testers. They will get concrete feedback about the current state of their system. This review is planned once in every two or three weeks so the customer can easily steer the development.
Feedback from the team: When customers come up with new requirements in the planning game the team directly gives an estimation of the time that it will take to implement.
Feedback is closely related to communication and simplicity. Flaws in the system are easily communicated by writing a unit test that proves a certain piece of code will break. The direct feedback from the system tells programmers to recode this part. A customer is able to test the system periodically according to the functional requirements, known as user stories.[5] To quote Kent Beck, "Optimism is an occupational hazard of programming. Feedback is the treatment."[9]
Courage[edit]
Several practices embody courage. One is the commandment to always design and code for today and not for tomorrow. This is an effort to avoid getting bogged down in design and requiring a lot of effort to implement anything else. Courage enables developers to feel comfortable with refactoring their code when necessary.[5] This means reviewing the existing system and modifying it so that future changes can be implemented more easily. Another example of courage is knowing when to throw code away: courage to remove source code that is obsolete, no matter how much effort was used to create that source code. Also, courage means persistence: A programmer might be stuck on a complex problem for an entire day, then solve the problem quickly the next day, but only if they are persistent.
Respect[edit]
The respect value includes respect for others as well as self-respect. Programmers should never commit changes that break compilation, that make existing unit-tests fail, or that otherwise delay the work of their peers. Members respect their own work by always striving for high quality and seeking for the best design for the solution at hand through refactoring.
Adopting the four earlier values leads to respect gained from others in the team. Nobody on the team should feel unappreciated or ignored. This ensures a high level of motivation and encourages loyalty toward the team and toward the goal of the project. This value is dependent upon the other values, and is oriented toward teamwork.
Rules[edit]
The first version of rules for XP was published in 1999 by Don Wells[10] at the XP website. 29 rules are given in the categories of planning, managing, designing, coding, and testing. Planning, managing and designing are called out explicitly to counter claims that XP doesn't support those activities.
Another version of XP rules was proposed by Ken Auer[11] in XP/Agile Universe 2003. He felt XP was defined by its rules, not its practices (which are subject to more variation and ambiguity). He defined two categories: "Rules of Engagement" which dictate the environment in which software development can take place effectively, and "Rules of Play" which define the minute-by-minute activities and rules within the framework of the Rules of Engagement.
Principles[edit]
The principles that form the basis of XP are based on the values just described and are intended to foster decisions in a system development project. The principles are intended to be more concrete than the values and more easily translated to guidance in a practical situation.
Feedback[edit]
Extreme programming sees feedback as most useful if it is done frequently and promptly. It stresses that minimal delay between an action and its feedback is critical to learning and making changes. Unlike traditional system development methods, contact with the customer occurs in more frequent iterations. The customer has clear insight into the system that is being developed, and can give feedback and steer the development as needed. With frequent feedback from the customer, a mistaken design decision made by the developer will be noticed and corrected quickly, before the developer spends much time implementing it.
Unit tests contribute to the rapid feedback principle. When writing code, running the unit test provides direct feedback as to how the system reacts to the changes made. This includes running not only the unit tests that test the developer's code, but running in addition all unit tests against all the software, using an automated process that can be initiated by a single command. That way, if the developer's changes cause a failure in some other portion of the system that the developer knows little or nothing about, the automated all-unit-test suite will reveal the failure immediately, alerting the developer of the incompatibility of their change with other parts of the system, and the necessity of removing or modifying their change. Under traditional development practices, the absence of an automated, comprehensive unit-test suite meant that such a code change, assumed harmless by the developer, would have been left in place, appearing only during integration testing – or worse, only in production; and determining which code change caused the problem, among all the changes made by all the developers during the weeks or even months previous to integration testing, was a formidable task.
Assuming simplicity[edit]
This is about treating every problem as if its solution were "extremely simple". Traditional system development methods say to plan for the future and to code for reusability. Extreme programming rejects these ideas.
The advocates of extreme programming say that making big changes all at once does not work. Extreme programming applies incremental changes: for example, a system might have small releases every three weeks. When many little steps are made, the customer has more control over the development process and the system that is being developed.
Embracing change[edit]
The principle of embracing change is about not working against changes but embracing them. For instance, if at one of the iterative meetings it appears that the customer's requirements have changed dramatically, programmers are to embrace this and plan the new requirements for the next iteration.
Practices[edit]
Further information: Extreme programming practices
Extreme programming has been described as having 12 practices, grouped into four areas:
Fine-scale feedback[edit]
Pair programming[5]
Planning game
Test-driven development
Extreme programming practices
Continuous process[edit]
Continuous integration
Refactoring or design improvement[5]
Small releases
Shared understanding[edit]
Coding standards
Collective code ownership[5]
Simple design[5]
System metaphor
Programmer welfare[edit]
Sustainable pace
Coding[edit]
The customer is always available
Code the unit test first
Only one pair integrates code at a time
Leave optimization until last
No overtime
Testing[edit]
All code must have unit tests
All code must pass all unit tests before it can be released.
When a bug is found, tests are created before the bug is addressed (a bug is not an error in logic, it is a test that was not written)
Acceptance tests are run often and the results are published
Controversial aspects[edit]
The practices in XP have been heavily debated.[5] Proponents of extreme programming claim that by having the on-site customer[5] request changes informally, the process becomes flexible, and saves the cost of formal overhead. Critics of XP claim this can lead to costly rework and project scope creep beyond what was previously agreed or funded.
Change-control boards are a sign that there are potential conflicts in project objectives and constraints between multiple users. XP's expedited methods are somewhat dependent on programmers being able to assume a unified client viewpoint so the programmer can concentrate on coding, rather than documentation of compromise objectives and constraints. This also applies when multiple programming organizations are involved, particularly organizations which compete for shares of projects.[citation needed]
Other potentially controversial aspects of extreme programming include:
Requirements are expressed as automated acceptance tests rather than specification documents.
Requirements are defined incrementally, rather than trying to get them all in advance.
Software developers are usually required to work in pairs.
There is no Big Design Up Front. Most of the design activity takes place on the fly and incrementally, starting with "the simplest thing that could possibly work" and adding complexity only when it's required by failing tests. Critics compare this to "debugging a system into appearance" and fear this will result in more re-design effort than only re-designing when requirements change.
A customer representative is attached to the project. This role can become a single-point-of-failure for the project, and some people have found it to be a source of stress. Also, there is the danger of micro-management by a non-technical representative trying to dictate the use of technical software features and architecture.
Dependence upon all other aspects of XP: "XP is like a ring of poisonous snakes, daisy-chained together. All it takes is for one of them to wriggle loose, and you've got a very angry, poisonous snake heading your way."[12]
Critics have noted several potential drawbacks,[5] including problems with unstable requirements, no documented compromises of user conflicts, and a lack of an overall design specification or document.
Scalability[edit]
Historically, XP only works on teams of twelve or fewer people. One way to circumvent this limitation is to break up the project into smaller pieces and the team into smaller groups. It has been claimed that XP has been used successfully on teams of over a hundred developers.[citation needed] ThoughtWorks has claimed reasonable success on distributed XP projects with up to sixty people.[citation needed]
In 2004, industrial extreme programming (IXP)[13] was introduced as an evolution of XP. It is intended to bring the ability to work in large and distributed teams. It now has 23 practices and flexible values.
Severability and responses[edit]
In 2003, Matt Stephens and Doug Rosenberg published Extreme Programming Refactored: The Case Against XP, which questioned the value of the XP process and suggested ways in which it could be improved.[6] This triggered a lengthy debate in articles, Internet newsgroups, and web-site chat areas. The core argument of the book is that XP's practices are interdependent but that few practical organizations are willing/able to adopt all the practices; therefore the entire process fails. The book also makes other criticisms, and it draws a likeness of XP's "collective ownership" model to socialism in a negative manner.
Certain aspects of XP have changed since the publication of Extreme Programming Refactored; in particular, XP now accommodates modifications to the practices as long as the required objectives are still met. XP also uses increasingly generic terms for processes. Some argue that these changes invalidate previous criticisms; others claim that this is simply watering the process down.
Other authors have tried to reconcile XP with the older methodologies in order to form a unified methodology. Some of these XP sought to replace, such as the waterfall methodology; example: Project Lifecycles: Waterfall, Rapid Application Development, and All That. JPMorgan Chase & Co. tried combining XP with the computer programming methods of capability maturity model integration (CMMI), and Six Sigma. They found that the three systems reinforced each other well, leading to better development, and did not mutually contradict.[14]
Criticism[edit]
Extreme programming's initial buzz and controversial tenets, such as pair programming and continuous design, have attracted particular criticisms, such as the ones coming from McBreen[15] and Boehm and Turner.,[16] Matt Stephens and Doug Rosenberg.[17] Many of the criticisms, however, are believed by Agile practitioners to be misunderstandings of agile development.[18]
In particular, extreme programming has been reviewed and critiqued by Matt Stephens's and Doug Rosenberg's Extreme Programming Refactored.[6][19]
Criticisms include:
a methodology is only as effective as the people involved, Agile does not solve this
often used as a means to bleed money from customers through lack of defining a deliverable product
lack of structure and necessary documentation
only works with senior-level developers
incorporates insufficient software design
requires meetings at frequent intervals at enormous expense to customers
requires too much cultural change to adopt
can lead to more difficult contractual negotiations
can be very inefficient; if the requirements for one area of code change through various iterations, the same programming may need to be done several times over. Whereas if a plan were there to be followed, a single area of code is expected to be written once.
impossible to develop realistic estimates of work effort needed to provide a quote, because at the beginning of the project no one knows the entire scope/requirements
can increase the risk of scope creep due to the lack of detailed requirements documentation
Agile is feature-driven; non-functional quality attributes are hard to represent as user stories.
See also[edit]
Agile software development
Continuous obsolescence
EXtreme Manufacturing
Extreme project management
Extreme programming practices
Kaizen
List of software development philosophies
Pair programming
Scrum (development)
Software engineering
Software craftsmanship
Stand-up meeting
Timeboxing
References[edit]
Jump up ^ "Human Centred Technology Workshop 2005", 2005, PDF webpage: Informatics-UK-report-cdrp585[permanent dead link].
^ Jump up to: a b "Design Patterns and Refactoring", University of Pennsylvania, 2003, webpage: UPenn-Lectures-design-patterns.
^ Jump up to: a b "Extreme Programming" USFCA-edu-601-lecture.
Jump up ^ "Manifesto for Agile Software Development", Agile Alliance, 2001, webpage: Manifesto-for-Agile-Software-Dev
^ Jump up to: a b c d e f g h i j k l m "Extreme Programming", Computerworld (online), December 2001, webpage: Computerworld-appdev-92.
^ Jump up to: a b c Rosenberg, Doug; Stephens, Matt (2003). Extreme Programming Refactored: The Case Against XP. Apress. ISBN 1-59059-096-1.
Jump up ^ "Interview with Kent Beck and Martin Fowler". informit.com.
Jump up ^ "Everyone's a Programmer" by Clair Tristram. Technology Review, November 2003. p. 39.
Jump up ^ Beck, K. (1999). Extreme Programming Explained: Embrace Change. Addison-Wesley. ISBN 978-0-321-27865-4.
Jump up ^ "Extreme Programming Rules". extremeprogramming.org.
Jump up ^ Ken Auer Archived September 20, 2008, at the Wayback Machine.
Jump up ^ "Extreme Programming explained: What we really think of XP". softwarereality.com.
Jump up ^ Cutter Consortium. "Industrial XP: Making XP Work in Large Organizations - Cutter Consortium". cutter.com.
Jump up ^ Extreme Programming (XP) Six Sigma CMMI.
Jump up ^ McBreen, P. (2003). Questioning Extreme Programming. Boston, MA: Addison-Wesley. ISBN 0-201-84457-5.
Jump up ^ Boehm, B.; R. Turner (2004). Balancing Agility and Discipline: A Guide for the Perplexed. Boston, MA: Addison-Wesley. ISBN 0-321-18612-5.
Jump up ^ Stephens, Matt; Doug Rosenberg (2004). The irony of extreme programming. , MA: Dr Dobbs journal.
Jump up ^ sdmagazine Archived March 16, 2006, at the Wayback Machine.
Jump up ^ Extreme Programming Refactored, Matt Stephens and Doug Rosenberg, Publisher: Apress L.P.
Further reading[edit]
Ken Auer and Roy Miller. Extreme Programming Applied: Playing To Win, Addison–Wesley.
Kent Beck: Extreme Programming Explained: Embrace Change, Addison–Wesley.
Kent Beck and Martin Fowler: Planning Extreme Programming, Addison–Wesley.
Kent Beck and Cynthia Andres. Extreme Programming Explained: Embrace Change, Second Edition, Addison–Wesley.
Alistair Cockburn: Agile Software Development, Addison–Wesley.
Martin Fowler: Refactoring: Improving the Design of Existing Code, Addison–Wesley.
Harvey Herela (2005). Case Study: The Chrysler Comprehensive Compensation System. Galen Lab, U.C. Irvine.
Jim Highsmith. Agile Software Development Ecosystems, Addison–Wesley.
Ron Jeffries, Ann Anderson and Chet Hendrickson (2000), Extreme Programming Installed, Addison–Wesley.
Craig Larman & V. Basili (2003). "Iterative and Incremental Development: A Brief History", Computer (IEEE Computer Society) 36 (6): 47–56.
Matt Stephens and Doug Rosenberg (2003). Extreme Programming Refactored: The Case Against XP, Apress.
Waldner, JB. (2008). "Nanocomputers and Swarm Intelligence". In: ISTE, 225–256.
Further reading[edit]
Ken Auer; Ron Jeffries; Jeff Canna; Glen B. Alleman; Lisa Crispin; Janet Gregory (2002). "Are Testers eXtinct? How Can Testers Contribute to XP Teams?". Springer-Verlag.
External links[edit]
Wikimedia Commons has media related to Extreme Programming.
Wikiquote has quotations related to: Extreme programming
Extreme Programming
A gentle introduction
Industrial eXtreme Programming
XP magazine
Problems and Solutions to XP implementation
Using an Agile Software Process with Offshore Development – ThoughtWorks' experiences with implementing XP in large distributed projects
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