Recipes in this chapter

• Architectural trade studies
• Architectural merge
• Pattern-driven architecture
• Subsystem and component architecture
• Architectural allocation
• Creating subsystem interfaces from use case scenarios
• Specializing a reference architecture

System analysis pays attention to the required properties of a system (such as its functionality), while system design focuses on how to implement a system that implements those needs effectively. Many different designs that can realize the same functionality; system engineers must select from among the possible designs based on how well they optimize crucial system properties. The degree of optimization is determined by examining with Measures of Effectiveness (MoE) applied to the design. Design is all about optimization, and architecture is no different. Architecture is the integration of high-level design concerns that organize and orchestrate the overall structure and behavior...

Five critical views of architecture

The Harmony process defines six critical views of architecture, as shown in Figure 3.1. Each view focuses on a different aspect of the largest scale optimization concerns of the system:

• Subsystem/Component Architecture is about the identification of subsystems, the allocation of responsibilities to the subsystems, and the specification of their interfaces.
• Distribution Architecture selects the means by which distributed parts of the system nteract, including middleware and communication protocols; this includes, but is not limited to, network architecture.
• Concurrency and Resource Architecture details the set of concurrency regions (threads and processes), how semantic elements map into those concurrency regions, how they are scheduled, and how they effectively share and manage shared resources.
• Data Architecture focuses on how data is managed. It includes technical means and policies for data storage, backup, retrieval...

Architectural trade studies

Trade studies are specifically concerned with the merit-based selection of approach or technology based on important concerns specific to the system development, system environment, or stakeholder needs. At a very fundamental level, trade studies are about making design choices to optimize important properties of the system at the expense of properties deemed less critical. To effectively perform trade studies, it is important to identify the things that can be optimized, the aspects subject to optimization, the MoE, and a set of alternatives to be evaluated.

Purpose

The purpose of performing an architectural trade study is to select an optimal design solution from a set of alternatives.

Inputs and preconditions

The inputs to this recipe are:

1. Functionality of concern, scoped as a set of requirements and/or use cases
2. Design options capable of achieving that functionality

Outputs and postconditions

The primary...

Creating subsystem interfaces from use case scenarios

There are many methods by which subsystem interfaces can be created. For example, a common approach is to refine the black box activity diagrams from the use case analyses into so-called white box activity diagrams with activity partitions representing the subsystems. When control flows cross into other swim lanes, the flow or service invocation is added to the relevant subsystem interface. Another common approach is to do the same thing but use the use case sequence diagrams rather than the activity diagrams. The advantage of these approaches is that they tie back into the use case analysis. It is also possible to create the interfaces de novo from the allocation of system features to the subsystems.

This recipe focuses on using sequence diagrams in the creation of the system interfaces. One advantage of this approach is that this approach can leverage sequence diagrams created from the execution of the use case models that...

Specializing a reference architecture

In this recipe, we will discuss the first of two approaches for using a reference architecture.

What is a reference architecture?

In Chapter 1, Basics of Agile Systems Modeling, we defined architecture as “the set of strategic design optimization decisions for the system.” The use of the word strategic here is important; these are design decisions that affect most or all subsystems and impact the overall performance and structure of the system. In the previous discussions, we went on to identify the six key views of architecture: the subsystem and component view, the concurrency and resource view, the distribution view, the data view, the dependability view, and the deployment view.

In the Pattern-driven architecture recipe in this chapter, we talked about how an architecture is an instantiation of patterns. In fact, a systems architecture is an integration of one or more patterns in each of the architectural viewpoints...