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ClearCase was developed by [[Atria Software]] and first released in 1992<ref>{{cite web | url = https://web.archive.org/web/20090802071539/https://www.findarticles.com/p/articles/mi_m0SMG/is_n13_v12/ai_12606942 | title = ClearCase - Atria Software Inc.'s software configuration management system - New Products: Development Tools - Brief Article - Product Announcement | publisher = Software Magazine | date = September 15, 1992 | access-date = 2007-12-01 }}</ref> on Unix and later on [[Windows]]. Some of the Atria developers had worked on an earlier, similar system: ''DSEE'' ([[Apollo Domain|Domain]] Software Engineering Environment) from [[Apollo Computer]]. After [[Hewlett-Packard]] bought [[Apollo Computer]] in 1989, those developers left to form Atria.<ref>{{cite web | url = http://www.cmcrossroads.com/cgi-bin/cmwiki/view/CM/HistoryOfCM | title = Key dates in Hardware/Software Configuration Management History | publisher = CM Crossroads LLC | year = 2007 }}</ref><ref>{{cite web | url = https://web.archive.org/web/20090802063953/https://www.findarticles.com/p/articles/mi_m0SMG/is_n8_v15/ai_17338017 | title = Complex development earns Atria an IS role; hot Unix vendor's move to Windows and NT opens IS doors - Company Profile | author = Michael Bucken | date = August 1995 | publisher = Software Magazine }}</ref><ref>{{cite newsgroup | url = http://lists.gnu.org/archive/html/info-cvs/2004-12/msg00237.html | title = Re: cvs vs. clearcase? | author = Andrew DeFaria | date = December 21, 2004 }}</ref> Atria later merged with [[Pure Software]] to form PureAtria<ref>{{cite web | url = https://query.nytimes.com/gst/fullpage.html?res=940CE6DE1639F934A35755C0A960958260 | title = Pure Software To Buy Astria In Stock Deal<!-- original article misspells Atria in title --> | author = Lawrence M. Fisher | date = June 7, 1996 | work = The New York Times | access-date = 2007-12-01 }}</ref> in 1996. That firm was acquired by [[Rational Software]] in 1997, which was purchased by [[IBM]] in 2003.<ref>{{ cite web | url = http://www-03.ibm.com/press/us/en/pressrelease/243.wss | title = IBM Reports 2003 First-Quarter Results | date = April 14, 2003 | publisher = IBM | access-date = 2008-01-09 }}</ref> IBM continues to develop and market ClearCase. In September 2016, IBM announced a strategic partnership with HCL Technologies that will allow for accelerated development.
DSEE introduced many concepts that were adopted by ClearCase. The Apollo Domain file system allowed special handler programs to intervene during file access. DSEE made use of this feature to invisibly substitute a versioned copy when a particular file was opened.<ref>{{cite web |url = https://web.archive.org/web/20070224072638/https://www.findarticles.com/p/articles/mi_m0HPJ/is_n3_v42/ai_10916486 |title = DSEE: a software configuration management tool |author = David c. Lubkin |date = June 1991 |publisher = Hewlett-Packard Journal |access-date = July 17, 2010 }}</ref> With the versioning specification resident in the user environment, all accesses to versioned files were redirected, including such mundane accesses as printing, viewing in a generic text editor etc.▼
DSEE relied heavily on a file that described all the software modules and their dependencies. The file had to be generated manually, which was a major impediment to its use in large systems. However, once generated, it enabled DSEE to calculate the optimum way to perform a build, re-using all modules that had previously been processed and whose version specifications matched the specifications for the build.▼
DSEE also introduced the "version spec," which was called a "thread." This was a list of possible versions that could be in the user environment or in a build. A major innovation was the use of build signatures and software release signatures in the thread. The items in a thread might thus be:▼
* Any copies reserved for editing (i.e. checked out)▼
* The latest version (usually for developers only)▼
* A branched version of a file (a version on an alternate line of development).▼
* A labeled version (for developers working on a particular revision level)▼
* The version used in build XYZ.▼
* The version used in software release x.y.z.▼
Threads were processed from top to bottom for each file. A developer thread might have "reserved" at the top, followed by a labeled version. For a fix to an existing release, the thread would be "reserved", then the release signature.▼
In the absence of the invisible file redirection of the Apollo Domain file system, ClearCase uses the virtual file system provided by the [[MultiVersion File System|MVFS]] feature that is described below. The "thread" concept corresponds to the ''dynamic view''. Support for derived objects in a view is similar to DSEE's concept.▼
== Infrastructure ==
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ClearCase MultiSite enables developers at different locations to use the same ClearCase versioned object base (VOB). Each ___location (site) has its own copy (replica) of the VOB. Data synchronization via any protocol can be unidirectional or bidirectional. Synchronization patterns can be one-to-one (two replicas exchange data), ring (round-robin synchronization), one-to-many (replication from a “hub” VOB) or many-to-many (each replica exchanges data with all other replicas).
== DSEE ==
▲DSEE (Domain Software Engineering Environment) introduced many concepts that were adopted by ClearCase. The Apollo Domain file system allowed special handler programs to intervene during file access. DSEE made use of this feature to invisibly substitute a versioned copy when a particular file was opened.<ref>{{cite web |url = https://web.archive.org/web/20070224072638/https://www.findarticles.com/p/articles/mi_m0HPJ/is_n3_v42/ai_10916486 |title = DSEE: a software configuration management tool |author = David c. Lubkin |date = June 1991 |publisher = Hewlett-Packard Journal |access-date = July 17, 2010 }}</ref> With the versioning specification resident in the user environment, all accesses to versioned files were redirected, including such mundane accesses as printing, viewing in a generic text editor etc.
▲DSEE relied heavily on a file that described all the software modules and their dependencies. The file had to be generated manually, which was a major impediment to its use in large systems. However, once generated, it enabled DSEE to calculate the optimum way to perform a build, re-using all modules that had previously been processed and whose version specifications matched the specifications for the build.
▲DSEE also introduced the "version spec," which was called a "thread." This was a list of possible versions that could be in the user environment or in a build. A major innovation was the use of build signatures and software release signatures in the thread. The items in a thread might thus be:
▲* Any copies reserved for editing (i.e. checked out)
▲* The latest version (usually for developers only)
▲* A branched version of a file (a version on an alternate line of development).
▲* A labeled version (for developers working on a particular revision level)
▲* The version used in build XYZ.
▲* The version used in software release x.y.z.
▲Threads were processed from top to bottom for each file. A developer thread might have "reserved" at the top, followed by a labeled version. For a fix to an existing release, the thread would be "reserved", then the release signature.
▲In the absence of the invisible file redirection of the Apollo Domain file system, ClearCase uses the virtual file system provided by the [[MultiVersion File System|MVFS]] feature that is described below. The "thread" concept corresponds to the ''dynamic view''. Support for derived objects in a view is similar to DSEE's concept.
== Releases ==
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