10.1 Patterns Management

Pattern Hierarchy

Patterns range from abstract to concrete. Abstract patterns represent concepts without physical references (i.e., are not available to the senses). Concrete refers to objects that are available to the senses. For example, freedom is abstract, but the book (on freedom) is concrete.

Design-centric patterns are organized in a pattern hierarchy that includes architectural styles, architectural patterns, and design patterns. An abstract pattern located at the top of the pattern hierarchy is called an architectural style; it captures a set of characteristics and features that make a structure identifiable. Styles are designed to capture knowledge of effective design for achieving specified goals within a particular context. An architectural pattern conforms to specific architectural styles and embodies architecture design decisions that are applicable to recurring design problems. They provide parameterized templates that can be adapted to provide solutions that are suitable to different development context. Design patterns conform to specific architectural patterns and provide granular design components to articulate them.

Once a technology stack that picks specific technologies that should be used to implement the solution has been selected, design-centric patterns can be implemented. Each technology stack has a corresponding implementation-centric pattern hierarchy² that includes implementation styles, implementation patterns, and idioms. An idiom is a phrase or expression whose meaning cannot be inferred from the literal definitions of its individual words, but instead is understood through common usage within a language.

Solution architects create several complex processes to successfully implement a business solution. These steps are:

1. Study the elements of technology that can be applied to solve a specific problem.
2. Propose a combination of building blocks for the best possible fix to the problem.
3. Design a solution and manage the implementation.

After the solution architect finalizes the design and implementation of the solution, the enterprise architects verify that the information technology strategy is aligned with the enterprise mission by analyzing the business properties. Enterprise and solution architects use pattern hierarchies to create best practices for business and technical architectures that guide the implementation of solutions to business problems. Generalization and information hiding are used to keep more abstract patterns at the top of the hierarchy. The technology that allows the management of architecture results from decades of research in patterns management and frameworks used to plan and deliver solutions that meet business and technology strategies.

Analysis and Design Model Patterns

A blueprint is a high-level plan used in the development stage, and an enterprise architecture (EA) is a conceptual blueprint that defines the structure and operation of organizations. Design modeling provides a variety of different views of the system like architecture plans for the enterprise. Examples of a design-centric architectural style are microservices. An example of a corresponding implementation-centric implementation style is REST Services. When the problem appears, an architectural pattern embodies architectural design decisions that are applicable to a recurring design problem parameterized to account for different solution development contexts.

A design pattern relates to common design structures and practices that enable the creation of reusable software. An example of a design pattern is a singleton. A singleton restricts the instantiation of a class and ensures that only one instance of the class exists (e.g., a scoreboard object in a game should be derived from a singleton class to ensure that there is only one scoreboard object and one set of scores for the players at any given time). The enterprise architecture scope includes:

• Enterprise scope: higher-level patterns that can be applied to the overall structure of the enterprise
• Solution scope: the pattern that can be applied to a single solution or system
• Domain scope: the pattern that can be applied to a specific domain

A pattern hierarchy applies at all levels of scope, but variants of the higher-level patterns add additional embedded patterns that may be documented as a given enterprise architecture (EA) model, which gets described more specifically at the portfolio or system levels. This is similar to the map of the city being part of the map of a region within the map of the world, as shown in Figure 10.2.

Figure 10.2 A blueprint shows top-down enterprise levels: enterprise, portfolio, system, and subsystem. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Implementation Patterns

In object-oriented programming languages such as Java, a singleton class can have only one object at a time. The purpose of a singleton class is to restrict the number of object creations to only one, which ensures access control to resources. A Java singleton class (Figure 10.3) is a corresponding implementation-centric example of an idiom that implements a singleton design pattern and allows one instance of a Java class to exist, as in Figure 10.4.

Figure 10.3 The SingletonPatternDemo class accesses the Java singleton class SingleObject using the getInstance() method to return the object. showMessage will print the message. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Figure 10.4 A Java singleton class is a corresponding implementation-centric example of an idiom that implements a singleton design pattern and allows one instance of a Java class to exist. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Global Issues in Technology

Patterns of Solutions

Problems and the need for solutions vary depending on the region of the world where people are located. For example, economically developing regions like Africa or parts of the Middle East do not have fiber-optic networks as sophisticated as the ones deployed in Europe, where extensive investments in infrastructure have been made. This disparity impacts not only access to the Internet but also the potential for growth in education, technology, and health-care systems. As a result, solutions to these problems are tailored to address the unique needs in these regions. Addressing these needs might involve developing alternative solutions like satellite Internet or mobile broadband networks, which can provide connectivity. However, these solutions need to be cost-effective and scalable to ensure they meet the population’s needs.

Pattern Catalogs

From a top-down standpoint (e.g., enterprise, portfolio, or project), architecture may appear in different levels of focus. The architecture areas span the whole enterprise and include various domains of architecture, such as business, information, application, and technology domains. The enterprise domains in the three standpoints are illustrated in Figure 10.5.

Figure 10.5 The architecture areas span across the whole enterprise and include various domains of architecture, such as business, information, application, and technology domains. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Patterns may be described using a pattern taxonomy and stored in a pattern repository or catalog. A pattern catalog is a collection of patterns that are organized according to specific characteristics and according to how the relationships between them are defined. Figure 10.6 illustrates the general structure of a pattern catalog. A pattern catalog allows the bookkeeping of clusters of patterns at various levels of specialization (i.e., analysis and design model patterns versus implementation patterns).

Figure 10.6 The general structure of a pattern catalog allows the bookkeeping of clusters. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

One example of a business architecture pattern that includes a generalization of business service composition and a pattern used to describe the sequencing of business services is business service orchestration. If the data does not include data presentation, then business service orchestration provides additional logic to process this kind of data. Another example of a business architecture pattern that focuses on the observed sequence of messages exchanged by peer services when performing a unit of work is called business service choreography. Figure 10.7 illustrates how various business architecture design patterns (e.g., exchange, shipment, order, and payment) may be combined via inheritance and composition to create a “buyer-seller” design pattern.

Figure 10.7 Various business architecture design patterns, such as exchange, shipment, order, and payment, are combined via inheritance and composition to create a buyer-seller design pattern. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Implementation patterns are typically specific to technology stacks that are selected as part of the specialization of a solution design (i.e., a transition from analysis and design model to implementation architecture). Figure 10.8 illustrates how a pattern catalog is used to select the patterns and eventually create and deploy software engineering products at different project levels.

Figure 10.8 A pattern catalog can be used to select the pattern based on the architecture and solution view for the enterprise perspectives. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Pattern Languages

As we learned in Chapter 9 Software Engineering, a pattern language provides a connected view of how to apply one pattern in the presence of another.

Current State of Patterns Management

A series of “patterns” that create an organization chart for developing software is called patterns management. In software engineering, the detailed study of engineering to design, develop, and maintain software, Christopher Alexander, a well-known building architect, is regarded as the father of the Pattern Language movement. Eric Gamma, Martin Fowler, and several other contributors are all part of the large community that has been focusing on collecting and documenting software patterns over the past forty years. As a side note, the original wiki, the technology behind Wikipedia, resulted directly from Alexander’s work, according to its creator, Ward Cunningham. Christopher Alexander’s work has also influenced the development of Agile software development, which is an interactive approach to software development in order to deliver value to customers, and Scrum, which is a management framework that helps the development team organize the work to reach a specific goal. A framework is an implementation-specific skeletal subsystem for design work. A subsystem is a set of collaborating components that perform a given task included in software systems, and it is a separate entity within a software architecture.

Enterprise architects use four architecture domains and architecture views to handle hybrid domains (e.g., an information systems architecture is as an architectural view that spans across the application and data architectures and handles both control and data flows). Therefore, the applicability of patterns may be qualified according to the (combination of) domain(s) of architecture they apply to business architecture patterns or information systems patterns.

A more general view promotes the bookkeeping of architectures at various levels of abstraction as part of an architecture continuum, representing a structure composed of building blocks to reuse architecture assets that conform to a pattern language. The corresponding specializations are then organized in a solution (architecture) continuum. In this case, architectures used at the enterprise level in the industry and specific organizations are derived from foundation and common systems architectures, as shown in Figure 10.9, and then realized practically as solution architectures.

Figure 10.9 The Open Group Architecture Framework (TOGAF) foundation architecture contacts common systems architectures, which contacts industry and organization architectures. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)