Deltas and Versions

When you check in a version, SCCS records only the line-by-line differences between the text you check in and the previous version. This set of differences is known as a delta. The version that is retrieved by an edit or get is constructed from the accumulated deltas checked in so far.

The terms "delta" and "version" are often used synonymously. However, their meanings aren't exactly the same; it is possible to retrieve a version that omits selected deltas (see "Excluding Deltas from a Retrieved Version ").

SIDs

An SCCS delta ID, or SID, is the number used to represent a specific delta. This is a two-part number, with the parts separated by a dot ( . ). The SID of the initial delta is 1.1 by default. The first part of the SID is referred to as the release number, and the second, the level number. When you check in a delta, the level number is incremented automatically. The release number can be incremented as needed. SCCS also recognizes two additional fields for branch deltas (described under "Branches ").

Strictly speaking, an SID refers directly to a delta. However, it is often used to indicate the version constructed from a delta and its predecessors.

ID Keywords

SCCS recognizes and expands certain keywords in a source file, which you can use to include version-dependent information (such as the SID) into the text of the checked-in version. When the file is checked out for editing, ID keywords take the following form:

%C%

where C is a capital letter. When you check in the file, SCCS replaces the keywords with the information they stand for. For example, %I% expands to the SID of the current version.

You would typically include ID keywords either in a comment or in a string definition. If you do not include at least one ID keyword in your source file, SCCS issues the diagnostic:

No Id Keywords (cm7)

For more information about ID keywords, refer to "Incorporating Version-Dependent Information by Using ID Keywords ".