University:
California State University, Northridge
Course:
COMP 684 | Software Architecture and Design
Academic year:

2024
Views:

76

Pages:

17
Author:

Bryanna Richmond

Quality Models and Quality Attributes Part 3 Architecting with Quality Attributes  The quality attributes that can be addressed by an application’s architecture are:       Functionality Performance (efficiency) Modifiability Availability and reliability Usability Portability Functionality  It is the ability of the system or application to satisfy the purpose for which it was designed.  It is related to validity, correctness, interoperability, and security.  It drives the initial decomposition of the system.  It is the basis upon which all other quality attributes are specified Interoperability  It is the quality of a system that enables it to work with other systems.  It includes the quality to work with other systems not yet known. Security  It is the ability to enforce authorization, authentication, and deliberate denial of service attacks.  Security requirements can affect the functional decomposition of the system.- Performance (Efficiency)  It represents the responsiveness of the system (e.g., the time required to respond to events or the number of events processed in some period of time).  Some aspects of performance are architectural (the distribution of computations across components) and some are not (choices of algorithms).  Performance has been a driving factor in systems architecture and often compromises the achievement of other quality attributes. Resource Efficiency  One aspect of performance is the efficient utilization of resources.  The decomposition of a system into layers may impede the system’s ability to satisfy performance requirements. Modifiability  It is the ability to grow an architecture over time.  A modifiable architecture can have new features added without requiring architectural rework Availability and Reliability  Availability is an attribute that measures the proportion of time the system is up and running.  Reliability is an attribute that measures the system’s ability to continue operating over time.  Both are partially addressed by the architecture. Recoverability  It is the ability of a system to pick up where it left off after a shutdown or crash.  This might involve launching diagnostic programs to check the integrity of the system before the actual system launches. Usability  This typically refers to the usability with respect to the end user.  It can also address other system users such as system maintainers, operators, etc.  It is measured using scenarios. Portability  It is the ability to reuse a component in a different application or operating environment.  It can be considered as a special kind of modifiability.  Portability related attributes are:     Adaptability Installability Conformance Replaceability Portability (Cont’d)  Extensibility is another word for portability.  One way to satisfy the extensibility requirement is to produce a set of platform-independent architectural models. This forces the designer to consider the architecture from a platform-independent point of view. Architecting and Quality Models  The architectural practices used to address quality attributes include the use of patterns and heuristics.  Architectural styles are high-level architecture patterns that address a specific set of concerns or quality attributes.  Some views (and models) address particular quality attributes and not others. (E.g., use cases address functionality but not performance.) Architecting and Quality Models (Cont’d)  Some quality attributes cannot be entirely evaluated by inspecting the models alone; some require additional context information such as scenarios. (E.g., modifiability can not be address without specifying what is to be modified.) A set of modification scenarios must be supplied. Summary  Quality attributes are measurable or observable characteristics of products and processes.  The quality requirements specification gives quantitative or qualitative values for these attributes that must be satisfied by the executable system.  It is cost effective to evaluate models and other intermediate products with respect to quality attributes. Summary (Cont’d)  Not all quality attributes can be satisfied by architectural decisions.  Reasons why the use of quality attributes is not common.        Misunderstanding of their importance Inadequate languages for expressing them Inadequate specification of quality requirements in projects Inadequate modeling methods and notations Inherent difficulty in designing for quality attributes Lack of documented design and architectural patterns The fact that quality control is an afterthought on most projects

Quality Models and Quality Attributes, Part 3

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