Enterprise Architecture

The definition of an architecture used in ANSI/IEEE Std 1471-2000is: "the fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution."

An enterprise architecture (EA) is a conceptual tool that assists organizations with the understanding of their own structure and the way they work. It provides a map of the enterprise and is a route planner for business and technology change.

Normally an enterprise architecture takes the form of a comprehensive set of cohesive models that describe the structure and the functions of an enterprise. Important uses of it are in systematic technology planning and architecting, and in enhanced decision making.

The individual models in an EA are arranged in a logical manner, and this provides an ever-increasing level of detail about the enterprise, including:

• Its objectives and goals.
• Its processes and organization.
• Its systems and data.
• The technology used

Architecture Perspective

The information in the enterprise architecture can be viewed from many perspectives and it can satisfy many needs. Architectural users include business managers and analysts, system architects and designers, workflow and procedures analysts, logistics specialists, organizational analysts, and so on. These people require high-level summary information, detailed data, and all levels in between. These demands are met through the creation of conceptual views, logical analyzes, and physical implementations.

Four general perspectives are important and are commonly used enterprise architecture. These are the business, application, information, and technology perspectives.

The business perspective

The business perspective describes how a business works. It includes broad business strategies along with plans for moving the organization from its current state to an envisaged future state. It will typically include the following:

• The enterprise's high-level objectives and goals.
• The business processes carried out by the entire enterprise, or a significant portion of the enterprise.
• The business functions performed.
• Major organizational structures.
• The relationships between these elements.

The application architecture perspective

The application perspective defines the enterprise's application portfolio and is application-centered. This view will typically include:

• Descriptions of automated services that support the business processes.
• Descriptions of the interaction and interdependencies (interfaces) of the organization's application systems.
• Plans for developing new applications and revising old applications based on the enterprises objectives, goals, and evolving technology platforms.

The application perspective may represent cross-organization services, information, and functionality, linking users of different skills and job functions in order to achieve common business objectives.

The information architecture perspective

The information perspective describes what the organization needs to know to run its business processes and operations. It includes:

• Standard data models.
• Data management policies.
• Descriptions of the patterns of information production and consumption in the organization.

The information perspective also describes how data is bound into the work flow, including structured data stores such as databases, and unstructured data stores such as documents, spreadsheets, and presentations that exist throughout the organization.

The technology architecture perspective

The technology perspective lays out the hardware and software supporting the organization. It includes, but is not limited to:

• Desktop and server hardware.
• Operating systems.
• Network connectivity components.
• Printers.
• Modems.

The technology perspective provides a logical, vendor-independent description of infrastructure and system components that are necessary to support the application and information perspectives. It defines the set of technology standards and services needed to execute the business mission.

Although there can be many perspectives, there is only one enterprise architecture that the perspectives view. The value of the enterprise architecture is not in any one individual perspective, but in the relationships, interactions, and dependencies among perspectives.

While all the perspectives are key elements of the enterprise architecture, this document will focus on the application and technology enterprise architecture perspectives.

Application and Technology Architecture

The functional requirements of a software system describe the business value that the software delivers. For a weather service, a functional requirement might be stated as "given a well-formed message A as input, the service will return a message B correct for the time span and geographic location represented in message A."

An application architecture is the enterprise architecture of any automated services that support and implement such functional requirements, including the interfaces to the business and other applications. It describes the structure of an application and how that structure implements the functional requirements of the organization. Whilst there should ideally be one application architecture in an organization, in practice there are typically many different application architectures in a given enterprise architecture blueprint.

The operational requirements of a software system define the reliability, manageability, performance, security, and interoperability requirements of the software (to list just a few). Common examples might be that the service is only available to authorized subscribers, and that the service be functioning properly 99.999 percent of the time.

A technology architecture is the enterprise architecture of the hardware and software infrastructure that supports the organization and implements the operational (or non functional) requirements, particularly the application and information architectures of the organization. It describes the structure and inter-relationships of the technologies used, and how those technologies support the operational requirements of the organization.

A good technology enterprise architecture can provide security, availability, and reliability, and can support a variety of other operational requirements, but if the application architecture is not designed to take advantage of the characteristics of the technology, it can still perform poorly or be difficult to deploy and operate. Similarly, a well-designed application structure that matches business process requirements precisely—and has been constructed from reusable software components using the latest technology— may map poorly to an actual technology architecture configuration, with servers inappropriately configured to support the application architecture components and network hardware settings unable to support information flow. This shows that there is a relationship between the application enterprise architecture and the technology enterprise architecture: a good technology enterprise architecture is built to support the specific applications vital to the organization; a good application enterprise architecture leverages the technology architecture to deliver consistent performance across operational requirements.

 

 

Figure 1. Relationships between application and technology in enterprise architecture

Architecture Conceptual, Logical, and Physical Views

For all architectural perspectives there are various views of the architecture that are often classified as conceptual, logical, and physical views. Conceptual architecture views are the most abstract and tend to be described in terms that are most familiar to the enterprise (non-IT professional) users of the system. The conceptual view is used to define the functional requirements and the business users' view of the application to generate a business model. Logical architecture views show the main functional components and their relationships within a system independently of the technical architecture details of how the functionality is implemented. Architects create enterprise application models, which are logical views of the business architecture model, as they determine how to meet business objectives and requirements. The application architecture models represent the logical view of the architecture for an application. Physical architecture views are the least abstract and illustrate the specific implementation components and their architecture relationships. Each of the elements in the physical architecture view is implemented, normally by a design and development process, as a software or hardware system. This implementation architecture view is normally owned by the development or operations organizations within an organization and so is outside the scope of this document.

 

 

Figure 2. Enterprise Architectural views

There can be (and indeed, normally are) multiple views at each architecture level; for example, there is normally a logical application architecture view per application.These views are driven by sets of requirements and in turn generate input into design, development, setup, and operational processes and systems.

 

 

Figure 3. Enterprise Architecture views and patterns

The remainder of this guide will focus on application and technology architecture, their concepts and key patterns for construction of service-based applications architecture that exploit the emerging technology of Web services. The implementation area, including design, development, setup, deployment, and administration, while of vital importance in the overall system generation, is outside the scope of this document.

Application Architecture

As previously discussed, the application architecture provides three views: the conceptual, the logical, and the physical architecture. These views are used by architects to generate models within organizations that support and meet their business requirements. Ideally there is just one architecture model per view, but in reality there may be multiple models per view—the result of growth and change in organizations and technologies. However, the rationalization of these models to a minimum set is the key to the provision of both efficient and flexible organizations.

Conceptual architecture view

The conceptual view is used to define the business requirements and the business users' view of the application to generate a business model. Conceptual modeling techniques, such as use case analysis, activity diagrams, process design, and business entity modeling, help to build a description of the key business processes and the data they use, in way that emphasizes business objectives and requirements, and is free of implementation technology.

Logical architecture view

Architects create application models that are logical views of the business model as they determine how to meet business objectives and requirements. The application models represent the logical view of the enterprise architecture for an application.

Architects here are concerned with the overall structure of the application. They decide on the mapping of data management and process steps, they design the interactions between parts of the model in terms of logical messages and sequences, and they determine what data and state should be held by the model.

Physical architecture view

Each of the elements in the application model requires mapping to elements of real technologies. In this way application models are realized as implementation models. Part of this task is undertaken during conventional development when programmers write detailed business logic as code, but much of the implementation activities are properly classed as framework completion—a technique for development where much of the infrastructure of distributed applications and data management is handled by sophisticated frameworks that are extended by custom application logic and declarative control structures. Framework completion shields developers from the intricacies of, for instance, asynchronous message handling, and allows developers with modest skills to make effective contributions to the project.

Architecting and building these models for an organization at each of the different levels is clearly a considerable amount of work and effort. Additionally, the correct definition of these models is critical for an organization. An incorrect architectural model almost always results in serious design or operational issues such as scalability or reliability problems or, in the worst cases, project non-completion and business impact. Architects are looking for frameworks and roadmaps to assist them in creation and implementation of these models and to minimize the risks associated with the use of incorrect models.

There are two main types of architectural guidance and assistance that can be provided to architects to speed up model generation and minimize risk.

The first of these is a set of architectural concepts that provide:

• A common understanding and communication.
• Guidance as to how and when specific concepts should be used, and information about their attributes.
• An indication as to when these concepts will be realized and available, either in terms of guidance or real technology.

The second is a set of patterns, based on real-world experience harvested from a large number

 

 

Figure 4. Views of application architecture

Application Architecture: Conceptual View

In the past, applications have been built by integrating local system services such as file systems and device drivers. This model was very flexible in providing access to a rich set of development resources and precise control over how the application behaved; however, this was very error-prone, costly, and time-consuming.

Today, complex distributed applications are being constructed that integrate existing applications and services from all over their networks and then add unique value on top by using elements such as business entities, data entities, and façades. This enables developers to focus on delivering unique business value. The result is reduced time-to-market, higher developer productivity, and ultimately, higher-quality software. This has been a powerful architectural model for a number of years; however, it creates "application stovepipes" or "islands of information" that cause significant problems in architectural reuse.

We are entering the next phase of computing—a phase enabled by the Internet together with the concept of Web services, which enables the creation of powerful applications that can be used by anyone, anywhere. It increases the reach of applications and enables the continual delivery of software. In this context, software is a service—to subscribe to and use through a communication network.

.NET facilitates this idea by joining the tightly coupled, highly productive aspects of n-tier computing with the loosely coupled, message-oriented concepts of the Web. This style of computing is called XML Web services. It represents the next evolution of application development and is the basis for conceptual application architecture.

Web services are discrete units of application logic that expose message-based interfaces suitable for access across a network. Typically, services provide both the business logic and the state management relevant to the problem they are designed to solve. When designing services, your goal is to effectively encapsulate the logic and data associated with real-world processes, making intelligent choices about what to include and what to implement as separate services.

State manipulation is governed by business rules. Business rules are relatively stable algorithms, such as the method in which an invoice is totaled from an item list, and are typically implemented as application logic.

Services are governed by policy. Policies are less static than business rules and may be regional or customer-specific. Policies are typically driven from lookup tables at run time.

So a more complete definition of services might be, "Services are network-capable units of software that implement logic, manage state, communicate via messages, and are governed by policy."

This conceptual view of applications is covered in more detail in Application Architecture: Conceptual View.

Application Patterns

A pattern is a solution to a problem in a context. A pattern codifies specific knowledge collected from experience in a domain. An application pattern is an architectural-level pattern that defines best practices in architectural design for a specific application environment.

There are a number of different types and taxonomies of patterns that are outside the scope of this document, as is the definition and explanation of specific patterns. Many of the present architectural patterns can be used in Web services-based architectures, but there also are a number of new patterns that are created by the new constructs available in Web services.

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