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Rational ClearCase is a family of computer software tools that supports software configuration management (SCM) of source code and other software development assets. It includes revision control. ClearCase forms the basis for configuration management at large and medium-sized businesses and can accommodate projects with hundreds or thousands of developers. It is developed by IBM. ClearCase supports two configuration management models: UCM (Unified Change Management) and base ClearCase. UCM provides an out-of-the-box model while base ClearCase provides a basic infrastructure (UCM is built on base ClearCase). Both can be configured to support a wide variety of needs. ClearCase can accommodate large binary files, large numbers of files, and large repository sizes. It supports branching, labeling, and versioning of directories. == History == ClearCase was developed by Atria Software and first released in 1992 on Unix and later on Windows. Some of the Atria developers had worked on an earlier, similar system: ''DSEE'' (Domain Software Engineering Environment) from Apollo Computer. After Hewlett-Packard bought Apollo Computer in 1989, those developers left to form Atria.〔(【引用サイトリンク】 Key dates in Hardware/Software Configuration Management History )〕 Atria later merged with Pure Software to form PureAtria. That firm was acquired by Rational Software, which was purchased by IBM in 2003. IBM continues to develop and market ClearCase. 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. 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 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rational ClearCase is a family of computer software tools that supports software configuration management (SCM) of source code and other software development assets. It includes revision control. ClearCase forms the basis for configuration management at large and medium-sized businesses and can accommodate projects with hundreds or thousands of developers. It is developed by IBM.ClearCase supports two configuration management models: UCM (Unified Change Management) and base ClearCase. UCM provides an out-of-the-box model while base ClearCase provides a basic infrastructure (UCM is built on base ClearCase). Both can be configured to support a wide variety of needs.ClearCase can accommodate large binary files, large numbers of files, and large repository sizes. It supports branching, labeling, and versioning of directories.== History ==ClearCase was developed by Atria Software and first released in 1992 on Unix and later on Windows. Some of the Atria developers had worked on an earlier, similar system: ''DSEE'' (Domain Software Engineering Environment) from Apollo Computer. After Hewlett-Packard bought Apollo Computer in 1989, those developers left to form Atria.(【引用サイトリンク】 Key dates in Hardware/Software Configuration Management History ) Atria later merged with Pure Software to form PureAtria. That firm was acquired by Rational Software, which was purchased by IBM in 2003. IBM continues to develop and market ClearCase.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. 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 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.」の詳細全文を読む スポンサード リンク
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