ClearCase Overview for Beginners

What is ClearCase?

·        ClearCase is a program for software configuration management and version control of all types of files & directories (elements).

·        It enables parallel development on geographically distributed sites.

·        ClearCase runs in both Unix and Windows. There is two interfaces in UNIX, command line (CLI) and graphical (GUI).

·        It enables access to files and directories as usual, but if you would like to change elements you must use ClearCase.

·        The method to work with elements is check-out/edit/check-in.

What is a VOB?

·        A VOB (Version Object Base) is a database (repository) that stores version-controlled elements, such as source files, binary files, directories etc.

·        You must mount a VOB (make a connection) before accessing the elements in it.

·        A VOB can be mounted on some or all workstations.  A project can have more than one VOB.

·        ClearCase protects files in the VOB from accidental modification, thereby all the elements is stored as read-only.

·        Each VOB must have a descriptive name, called a VOB-tag. When accessing elements or working with VOBs, you use the VOB-tag. When listing VOBs you see the tag and the storage path like this:

       /vobs/cc_vobtest          /net/wrnsg03/export/vobs/vob1/cc_vobtest.vbs

      VOB-tag                  Storage path

What is a view

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Concepts

• VOB or Versioned Object Base: This is the permanent data repository of a development tree or subtree storing all file system elements. It is typically hosted on in the network on a remote host and mounted as an MVFS file system on the user’s machine.
• View: A view is what you use to access a VOB transparently. Without a view, the VOB appears to be empty.
• Elements,Branches,and Versions: A versioned file system object in a VOB is called an element. There can be multiple versions of each element logically organized into a hierarchical version tree containing multiple branches/sub-branches.
• Config Spec: A config spec is a document that contains a set of rules that is used by the view for selecting the versions of elements. A simplified explanation would be that a config spec is a filter that determines what versions of elements from the vob gets loaded into a view. Typically the Clearcase admin or project lead will provide you with a config spec and it looks somewhat like this:

########################################
# config spec:
# line1 - Select any files I have checked out
# line 2 - Ignore lost+found.
# line 3 - Select the LATEST element on the main branch
########################################
element       *      CHECKEDOUT
element      …/lost+found/…      -none
element      *     /main/LATEST

Of course, a real config spec is much larger and more complicated.