Three Dimensions of Product Line Engineering

Organizations building a portfolio of products have to deal with three distinct areas of concerns, shown in the illustration: Managing the lifecycle of each product (vertical axis); evolving the portfolio over time (horizontal axis); and managing the plurality of products (outward-pointing axis).

Product Line Engineering (PLE) addresses each of these "dimensions":

• The Multi-phase axis deals with the usual product engineering lifecycle concerns, such as requirements engineering, architecture and design, implementation, and test, plus the traceability for interdependency among the phases. The PLE characteristic of consistent variation management in artifacts from across the lifecycle supports product line diversity through variation points in all assets across the full lifecycle.

• The Multi-baseline axis deals with the usual temporal concerns of product engineering, such as version, configuration and change management. The PLE characteristic of CM that maintains assets (and not products) supports asset evolution for all assets, without having to independently manage the evolution of each of the products in a product line.

• The multi-product axis, of course, deals directly with the PLE concerns not supported by conventional product-centric engineering.

The multi-phase dimension

PLE enforces consistent treatment of the artifacts' variation points under the production infrastructure, so that a full set of demonstrably consistent supporting artifacts can be systematically generated for each product. This works because PLE employs a small, unified set of variation mechanisms that apply to any kind of asset, and the automation of a configurator to exercise those variation mechanisms consistently.

The illustration shows the classic V-model for systems and software engineering. Each phase is augmented by the addition of variation points (indicated by the gear symbol) to the artifacts native to that phase.

A Bill-of-Features™ for a product corresponds to the feature selections within the feature profiles for that product. The yellow arrows illustrate that all of the variation points in all of the artifacts across the full lifecycle are synchronously and consistently configured according to the single consolidated collection of feature selections in the Bill-of-Features.

The multi-baseline dimension

The most important aspect of CM in PLE is that the full superset of available PLE assets (and not the individual products or systems) are managed under CM. A new version of a product is not derived from a previous version of the same product, but from the shared superset of PLE assets themselves.

Previous approaches to configuration management for product lines have adopted a "multi-dimensional" approach, claiming that CM for product lines requires CM for core assets and CM for products and also stating that "CM for product lines is therefore more complex than it is for single systems". In fact, a key tenet of PLE is to reduce the complexity of product line CM to that for single products, and much less than that for a suite of separately-managed products.

Under the PLE factory paradigm, any defects are fixed in the shared assets, not the products. The affected products will then be re-generated.