I define a product line as a jointly managed set of products or services that share a common core. In addition, I include a configurable set of variants. Consequently, the product line meets needs of particular customers or market segments. For example, I may provide different models that share hardware and software building blocks. Moreover, I document the shared parts as commonalities. Furthermore, I record the differing parts as variability.
First, I highlight commonalities. They include features, components, and core assets that every product in the line reuses. Then, I specify variability. I identify variation points where I can choose one or more variants. For example, I call “different colors” or “different memory sizes” variation points. Likewise, I call each option at a variation point a variant. Therefore, a product in the line contains all commonalities and a selected set of variants.
I differentiate product line from product family. In particular, I explain that a product family groups connected products that complement each other. In contrast, I state that a product line groups substitutable product variants that differ in function or price. Moreover, some practitioners use the terms synonymously. Nevertheless, I keep the distinction when I design requirements and architecture.
I separate product line development into two clear processes. First, I perform domain engineering. There, I identify commonalities and variability across existing variants. Then, I create a product line model and core assets. Second, I perform application engineering. There, I derive specific products. In addition, I adapt the product line model to create a concrete variant. Consequently, I ensure traceability from core assets to the final product.
I manage requirements differently in a product line. For example, I use a requirements pool to store more requirements than any single product needs. Then, I select relevant requirements during application engineering. Moreover, I describe optional and alternative requirements as variants. Thus, I avoid writing a separate full specification for every product. Instead, I document variation points and selection rules.
I enforce selection and combination rules. Specifically, I define dependencies and constraints in the domain model. Therefore, I ensure that chosen variants produce an executable and consistent product. Otherwise, I risk incompatible combinations or missing features.
I point out practical benefits. Firstly, I reduce duplicated work. Secondly, I speed up product creation. Thirdly, I give stakeholders clear choices. For example, at elicitation, a client often cannot choose between solution A and solution B. In that case, I offer variants that differ in cost or time. Consequently, the client can decide later.
Finally, I provide a simple example. For instance, I treat a tablet family as a product line. I document housing, display, and processor as commonalities. Then, I set memory size, color, and wireless options as variation points. Thus, I derive concrete models like “64 GB, black, Wi‑Fi and 4G.” In summary, I use product lines to manage reuse, to capture variability, and to streamline requirements across multiple related products.