Software Engineering-Version Control

Version control combines procedures and tools to manage different versions of configuration objects that are created during the software process. Clemm describes version control in the context of SCM:

Configuration management allows a user to specify alternative configurations of the software system through the selection of appropriate versions. This is supported by associating attributes with each software version, and then allowing a configuration to be specified [and constructed] by describing the set of desired attributes.

These "attributes" mentioned can be as simple as a specific version number that is attached to each object or as complex as a string of Boolean variables (switches) that indicate specific types of functional changes that have been applied to the system.

One representation of the different versions of a system is the evolution graph . Each node on the graph is an aggregate object, that is, a complete version of the software. Each version of the software is a collection of SCIs (source code, documents, data), and each version may be composed of different variants.

To illustrate this concept, consider a version of a simple program that is composed of entities 1, 2, 3, 4, and 5.3 Entity 4 is used only when the software is implemented using color displays. Entity 5 is implemented when monochrome displays are available. Therefore, two variants of the version can be defined: (1) entities 1, 2, 3, and 4; (2) entities 1, 2, 3, and 5.

To construct the appropriate variant of a given version of a program, each entity can be assigned an "attribute-tuple"—a list of features that will define whether the entity should be used when a particular variant of a software version is to be constructed. One or more attributes is assigned for each variant. For example, a color attribute could be used to define which entity should be included when color displays are to be supported.

Another way to conceptualize the relationship between entities, variants and versions (revisions) is to represent them as an object pool .The relationship between configuration objects and entities, variants and versions can be represented in a three-dimensional space. An entity is composed of a collection of objects at the same revision level. A variant is a different collection of objects at the same revision level and therefore coexists in parallel with other variants. A new version is defined when major changes are made to one or more objects.

A number of different automated approaches to version control have been proposed over the past decade. The primary difference in approaches is the sophistication of the attributes that are used to construct specific versions and variants of a system and the mechanics of the process for construction.
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