1.6 Extended Namespace for Elements, Branches, and Versions

An element's version tree has the same form as a standard directory tree (Figure 6), which compares components of the version tree to components of a directory tree in extended namespace.

As a component of the version tree, the element is the root of the directory tree in the extended namespace. The element itself appears to be a directory, which contains a single subdirectory, corresponding to the main branch. (It can also contain some version labels.)

A branch in the version tree appears as a subdirectory in the extended namespace. As a directory, each branch can contain files (individual versions and version labels), directories (subbranches), and links (version labels).

A version in the version tree is a leaf name of the directory tree in the extended namespace. Each version of an element is a leaf of the directory tree. For a file element, the leaf contains text lines or binary data. For a directory element, the leaf contains a directory structure.

Figure 6 Version Tree and Extended Namespace

Accordingly, any location within an element's version tree can be identified by a pathname in this extended namespace:

Dynamic View Access Model

All ClearCase data is accessed through the MVFS, which, by default, occupies drive M: on each ClearCase host. Each active view has a name called a view-tag which appears in the root directory of M. Each active VOB has a path called a VOB-tag which appears as a subdirectory under each active view, as shown in Figure 7.

Figure 7 ClearCase MVFS Namespace

From drive M, you can access VOBs using pathnames of the following form:

\view-tag\vob-tag\pname-in-vob

Typically, however, you do not work directly on drive M, but in the view root directory accessed by a shortcut in ClearCase Explorer. In Windows Explorer, you typically assign a drive to a view.

Figure 8 shows how the MVFS namespace looks from a drive assigned to a view in the ClearCase Explorer view shortcut, with the net use command, or by clicking Tools > Map Network Drive in Windows Explorer.

Figure 8 The MVFS Namespace from a Drive

From any drive, you can specify view-extended pathnames of the following form:

M:\view-tag\vob-tag\pname-in-vob

If you move to drive M, you are in view-extended namespace, and all VOB access is by view-extended pathnames.

To eliminate any confusion that may result from unintentional use of view-extended pathnames when you are working at a command prompt, we recommend that you work from a drive letter assigned to a view. This permits you to use VOB pathnames of the following form:

drive-letter:\vob-tag\vob-object-pname

in both cleartool and standard operating system commands. Furthermore, this approach is required if you want to share DOs between views at build time.