Questions tagged [clearcase]

ClearCase (a.k.a. Rational ClearCase) is version control system (VCS), available commercially from IBM.

Defining features

• It is centralized rather than distributed: There is a central server (possibly replicated) holding the authoritative versions of data and their histories; a developer or user employs a client to access data on the central server, and cannot rely on other clients or on itself as an alternative to the server.
• It is network-oriented: Version histories and other meta-data is not to be found in some hidden subfolder on the local file system, and manipulated through edits to those files. Any interaction with such histories is carried out over connections to the ClearCase server.
• Versioning happens at file-level rather than repository-level. Thus, changes happen to individual files independently of others; when "viewing" a repository, one in fact sees a collection of different versions of many independent objects.
• It is closed-source, only available under a restrictive license.

Additional notworthy features

• Supports two kinds of access to repositories:

  • snapshot view: A local copy of (certain versions of) all files in a repository, pulled once from the server.
  • dynamic view: A dynamically-synched form of access to a repository, where all operations actually happen on the ClearCase server, and all writes and changes impact it.

  the distinction between the two view types is somewhat similar to the POP3 vs IMAP protocols in email, or NFS vs rsync'ed filesystems. In fact, dynamic views are implemented via operating system kernel integration of the ClearCase client.

• A complex mechanism of choosing which versions and branches of which files are used in a view, through a cascading/fall-through chain of rules called a config-spec (view configuration specification). These also determine when ClearCase is to create new versions of some files, in the same or in a new b ranch.

• Replication of the centrally-stored versioned data, for better robustness (the "MultiSite" feature), with various supported syncrhonization/replication patterns.

History

ClearCase was initially developed in the early 1990s by Atria software; Atria later merged into Rational Software; and Rational was eventually became a division of IBM, which bought it in 2003. ClearCase development/maintenance is ongoing, albeit slowly: over the past decade revisions have been released once a year or several years.

Online resources

• Product Homepage
• ClearCase Knowledge Center
• Forums
• Wikipedia entry