Editing IBM DevOps Code ClearCase (section)

== DSEE ==

DSEE (Domain Software Engineering Environment) 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.<ref>{{cite web |url = https://www.findarticles.com/p/articles/mi_m0HPJ/is_n3_v42/ai_10916486 |archive-url = https://web.archive.org/web/20070224072638/https://www.findarticles.com/p/articles/mi_m0HPJ/is_n3_v42/ai_10916486 |url-status = dead |archive-date = 2007-02-24 |title = DSEE: a software configuration management tool |author =  David c. Lubkin |date = June 1991 |publisher = Hewlett-Packard Journal |access-date  = July 17, 2010 }}</ref>  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 [[MultiVersion File System|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.