Thursday, March 25, 2010

Evaluating Application Architecture, Quantitatively



Evaluation of an application architecture is an important step in any architecture-definition process. Its level of significance varies from organization to organization, based on a variety of factors (such as application size and business criticality). In some IT organizations, it is a part of a formal process; in others, it is performed only upon special requests that stakeholders might raise. Enterprises sometimes have a dedicated “Architectural Review Board” (or ARB) that is made up of a team of experienced architects who are earmarked for performing periodic architectural evaluations.
Scenarios that drive the architecture-evaluation process include:
·         When a business must validate an application architecture to see whether it can support new business models.
·         An expansion to new geographies and regions—resulting in the need to check whether an existing application architecture can scale to new levels.
·         Impaired application performance and user concerns that lead to an assessment, to see whether it can be reengineered with minimal effort to ensure optimum performance.
·         Stakeholders having to ensure that a proposed application architecture will meet all technical and business goals—ensuring that key architectural decisions were made with key use cases/ architectural scenarios in mind and will meet the nonfunctional requirements of the application.

In the context of the new application development, the key objectives of carrying out an architecture-evaluation process are:
·         Avoiding costly redevelopment later in the software-development life-cycle (SDLC) process by detecting and correcting architectural flaws earlier.
·         Eliminating surprises and last-minute rework that is due to the suboptimal usage of technology options that are provided by platform vendors such as Microsoft.

Architectural reviews are also performed based on only a particular quality-of-service attribute—such as “Performance” or “Security”—for example, how secure the architecture is, whether an architecture has the potential to support a certain number of transactions per second, or whether an architecture will support such a specified time.
The application architectural-evaluation process involves a preliminary review, based on a checklist that is provided by the platform vendor and subsequent presentations, debates, brainstorming sessions, and whiteboard discussions among the architects. Key aspects of brainstorming sessions also include the outputs of the scenario-based evaluation exercises that are performed by using industry-standard methods such as the Architecture Trade-Off Analysis Method (ATAM), Software Architecture Analysis Method (SAAM), and Architecture Reviews for Intermediate Designs (ARID). There are also different methods that are available in the industry to assess the architectures, based exclusively on factors such as cost, modifiability, and interoperability.
The checklist that is provided by a platform vendor ensures the adoption of the right architectural patterns and appropriate design patterns. With its patterns & practices initiative, Microsoft provides a set of checklists/questionnaires across various crosscutting concerns for the evaluation of application architectures that are built on Microsoft’s platform and products. An architecture-evaluation process usually results in an evaluation report that contains qualitative statements such as, “The application has too many layers” or “The application cannot be scaled out, because the layers are tightly coupled.”
Instead of having qualitative statements, if the evaluation process ends up providing some metrics—such as a kidney-diagnosis process that ends with a “kidney number” or a lipid-profile analysis that ends with numerical figures for HDL and LDL—it will be easier for stakeholders to get a clear picture of the quality of the architecture.
This article outlines a framework for applying quantitative treatment to the architecture-evaluation process that results in more intuitive and quantitative output. This output will throw more light on areas of the application architecture that need refactoring or reengineering and will be more useful for further discussions and strategic decision making.

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