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Rational ClearCase is a software tool for revision control (configuration management, SCM etc) of source code and other software development assets. It is developed by the Rational Software division of IBM. more...

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ClearCase forms the base of version control for many large and medium sized businesses and can handle projects with hundreds or thousands of developers, but the price is quite steep for smaller companies.

Rational supports two types of SCM configurations, UCM, and base ClearCase. UCM provides an out-of-the-box SCM configuration while base ClearCase supplies only the basic tools. Both can be configured to support a wide variety of SCM needs.

ClearCase can run on a number of platforms including Linux, Solaris and Windows. It can handle large binary files, large numbers of files, and large repository sizes. It handles 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 system: DSEE (Domain Software Engineering Environment) from Apollo Computer. Atria later merged with Pure Software to form PureAtria. That firm merged with Rational Software, which was purchased by IBM. IBM continues to develop and market ClearCase. It is a popular product used by software production companies.

Views

Objects under version control in ClearCase are stored with their histories in repositories called VOBs (Versioned Object Base). ClearCase's novelty was in its versioned file system (called MVFS: MultiVersion File System), which can be used to mount VOBs as a virtual file system through a dynamic view, selecting a consistent set of versions and allowing for the production of derived objects. The dynamic view allows this to map to a Software Configuration. This was a departure from the repository/sandbox model, allowing for the early management of artifacts (before they are being checked in, and not limited to these first order configuration items).

Alternatively, ClearCase supports snapshot views which are just copies of a directory tree spanning one or several VOBs. Snapshot views do not use a virtual file system to provide access to VOB data. Instead, a snapshot view stores a copy of the VOB data locally on the user's computer. Snapshot views can be used while disconnected from the network and later resynchronized to the VOB when a connection is reestablished. This mode of operation is similar to how the widely-used CVS (Concurrent Versions System) software works.

From the perspective of software on the client computer, a view appears as just another file system. If a file is created in a view by normal OS means (copying or saving from an editor for instance), then ClearCase will create this file as a "view-private" file. It will not be visible in any other view. This allows build systems to operate in the same directory structure as the source code, and ensures that each developer can build completely independently of each other (though if the view is a dynamic one then the normal overhead associated with accessing files over an NFS link applies). A view-private file (or directory for that matter) can be converted into a versioned element at any time, making it visible to other developers.

Read more at Wikipedia.org