4.6 Business Qualities

In addition to the qualities that apply directly to a system, a number of business quality goals frequently shape a system's architecture. These goals center on cost, schedule, market, and marketing considerations. Each suffers from the same ambiguity that system qualities have, and they need to be made specific with scenarios in order to make them suitable for influencing the design process and to be made testable. Here, we present them as generalities, however, and leave the generation of scenarios as one of our discussion questions.

• Time to market. If there is competitive pressure or a short window of opportunity for a system or product, development time becomes important. This in turn leads to pressure to buy or otherwise re-use existing elements. Time to market is often reduced by using prebuilt elements such as commercial off-the-shelf (COTS) products or elements re-used from previous projects. The ability to insert or deploy a subset of the system depends on the decomposition of the system into elements.

• Cost and benefit. The development effort will naturally have a budget that must not be exceeded. Different architectures will yield different development costs. For instance, an architecture that relies on technology (or expertise with a technology) not resident in the developing organization will be more expensive to realize than one that takes advantage of assets already inhouse. An architecture that is highly flexible will typically be more costly to build than one that is rigid (although it will be less costly to maintain and modify).

• Projected lifetime of the system. If the system is intended to have a long lifetime, modifiability, scalability, and portability become important. But building in the additional infrastructure (such as a layer to support portability) will usually compromise time to market. On the other hand, a modifiable, extensible product is more likely to survive longer in the marketplace, extending its lifetime.

• Targeted market. For general-purpose (mass-market) software, the platforms on which a system runs as well as its feature set will determine the size of the potential market. Thus, portability and functionality are key to market share. Other qualities, such as performance, reliability, and usability also play a role. To attack a large market with a collection of related products, a product line approach should be considered in which a core of the system is common (frequently including provisions for portability) and around which layers of software of increasing specificity are constructed. Such an approach will be treated in Chapter 14, which discusses software product lines.

• Rollout schedule. If a product is to be introduced as base functionality with many features released later, the flexibility and customizability of the architecture are important. Particularly, the system must be constructed with ease of expansion and contraction in mind.

• Integration with legacy systems. If the new system has to integrate with existing systems, care must be taken to define appropriate integration mechanisms. This property is clearly of marketing importance but has substantial architectural implications. For example, the ability to integrate a legacy system with an HTTP server to make it accessible from the Web has been a marketing goal in many corporations over the past decade. The architectural constraints implied by this integration must be analyzed.