Basic Software Product Line Concepts

Software product lines can be described in terms of four simple concepts, as illustrated in the figure below:

• Software asset inputs: a collection of software assets – such as requirements, source code components, test cases, architecture, and documentation – that can be configured and composed in different ways to create all of the products in a product line. Each of the assets has a well defined role within a common architecture for the product line. To accommodate variation among the products, some of the assets may be optional and some of the assets may have internal variation points that can be configured in different ways to provide different behavior.
• Decision model and product decisions: The decision model describes optional and variable features for the products in the product line. Each product in the product line is uniquely defined by its product decisions - choices for each of the optional and variable features in the decision model.
• Production mechanism and process: the means for composing and configuring products from the software asset inputs. Product decisions are used during production to determine which software asset inputs to use and how to configure the variation points within those assets.
• Software product outputs: the collection of all products that can be produced for the product line. The scope of the product line is determined by the set of software product outputs that can be produced from the software assets and decision model.

Figure: Basic Software Product Line Concepts

These concepts illustrate the key objectives of software product lines: to capitalize on commonality and manage variation in order to reduce the time, effort, cost and complexity of creating and maintaining a product line of similar software systems.

• Capitalize on commonality through consolidation and sharing within the software asset inputs, thereby avoiding duplication and divergence.
• Manage variation by clearly defining the variation points and decision model, thereby making the location, rationale, and dependencies for variation explicit.

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