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What is Software Architecture?



Software application architecture is the process of defining a structured solution that meets all of the technical and operational requirements, while optimizing common quality attributes such as performance, security, and manageability. It involves a series of decisions based on a wide range of factors, and each of these decisions can have considerable impact on the quality, performance, maintainability, and overall success of the application.

Philippe Kruchten, Grady Booch, Kurt Bittner, and Rich Reitman derived and refined a definition of architecture based on work by Mary Shaw and David Garlan (Shaw and Garlan 1996). Their definition is:

“Software architecture encompasses the set of significant decisions about the organization of a software system including the selection of the structural elements and their interfaces by which the system is composed; behavior as specified in collaboration among those elements; composition of these structural and behavioral elements into larger subsystems; and an architectural style that guides this organization. Software architecture also involves functionality, usability, resilience, performance, reuse, comprehensibility, economic and technology constraints, tradeoffs and aesthetic concerns.”

In Patterns of Enterprise Application Architecture, Martin Fowler outlines some common recurring themes when explaining architecture. He identifies these themes as:

“The highest-level breakdown of a system into its parts; the decisions that are hard to change; there are multiple architectures in a system; what is architecturally significant can change over a system's lifetime; and, in the end, architecture boils down to whatever the important stuff is.”

[http://www.pearsonhighered.com/educator/academic/product/0,3110,0321127420,00.html]

In Software Architecture in Practice (2nd edition), Bass, Clements, and Kazman define architecture as follows:

“The software architecture of a program or computing system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationships among them. Architecture is concerned with the public side of interfaces; private details of elements—details having to do solely with internal implementation—are not architectural.”

[http://www.pearsonhighered.com/educator/academic/product/0,4096,0321154959,00.html]

Why is Architecture Important?

Like any other complex structure, software must be built on a solid foundation. Failing to consider key scenarios, failing to design for common problems, or failing to appreciate the long term consequences of key decisions can put your application at risk. Modern tools and platforms help to simplify the task of building applications, but they do not replace the need to design your application carefully, based on your specific scenarios and requirements. The risks exposed by poor architecture include software that is unstable, is unable to support existing or future business requirements, or is difficult to deploy or manage in a production environment.

Systems should be designed with consideration for the user, the system (the IT infrastructure), and the business goals. For each of these areas, you should outline key scenarios and identify important quality attributes (for example, reliability or scalability) and key areas of satisfaction and dissatisfaction. Where possible, develop and consider metrics that measure success in each of these areas.

 

Figure 1

User, business, and system goals

Tradeoffs are likely, and a balance must often be found between competing requirements across these three areas. For example, the overall user experience of the solution is very often a function of the business and the IT infrastructure, and changes in one or the other can significantly affect the resulting user experience. Similarly, changes in the user experience requirements can have significant impact on the business and IT infrastructure requirements. Performance might be a major user and business goal, but the system administrator may not be able to invest in the hardware required to meet that goal 100 percent of the time. A balance point might be to meet the goal only 80 percent of the time.

Architecture focuses on how the major elements and components within an application are used by, or interact with, other major elements and components within the application. The selection of data structures and algorithms or the implementation details of individual components are design concerns. Architecture and design concerns very often overlap. Rather than use hard and fast rules to distinguish between architecture and design, it makes sense to combine these two areas. In some cases, decisions are clearly more architectural in nature. In other cases, the decisions are more about design, and how they help you to realize that architecture.

By following the processes described in this guide, and using the information it contains, you will be able to construct architectural solutions that address all of the relevant concerns, can be deployed on your chosen infrastructure, and provide results that meet the original aims and objectives.

Consider the following high level concerns when thinking about software architecture:







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