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

2024
Views:

278

Pages:

22
Author:

Fennaumg

Quality Models and Quality Attributes Part 1 Outline  Process and product quality  Improving the quality of the process can improve the quality of the product.  Process quality does not address all qualities.  Specifying quality requirements  Some quality attributes can be quantifiably measured, others have qualitative values which are observed.  Understanding quality models  A quality model is a taxonomy of quality attributes and their relationships.  Architecting with quality attributes  Several quality attributes are influenced by the architecture. Process and Product Quality  Process qualities are a measure of an activity the end result of which is a product.  Few quality models for the software architecting process exist.  Product quality is a measure of a tangible product itself which could be the final executable system or intermediate products like specifications, models, plans, etc, which collectively form the architectural description. Specifying Quality Requirements  Sample questions to discover information about quality attributes:    How does the application fit into the enterprise’s objectives, processes, and other information systems? How does it relate to other systems including manual business processes? Is it intuitive and usable or does it sit in a virtual corner collecting cyber-dust? Specifying Quality Requirements (Cont’d)  A quality attribute is a property of a process or product that can have some qualitative or quantitative value and can be measured or observed.  Examples of quality attributes are:     Maintainability Portability Functionality usability Specifying Quality Requirements (Cont’d)  A quality requirement is a specification of the acceptable values of a quality attribute that must be present in the system.  By leaving certain attributes out of the requirements specification, it implies that these attributes are not important.  However, they were probably omitted due to lack of understanding of the quality or how to specify it. Specifying Quality Requirements (Cont’d)  The external view of an application’s qualities is called its characteristics (usability, performance, etc.).  Internal characteristics or subcharacteristics are quality attributes viewable by the developers (throughput, load balancing, fault tolerance, etc.).  One internal attribute may influence one or more characteristics.  One characteristic may be influenced by one or more internal attributes. Measuring Quality Attributes  A metric is a qualitative or quantitative measurement or scale or a specified quality attribute together with a method or technique for observing or measuring the quality.  Examples of internal metrics are the complexity of the code logic, or the performance of specific functions.  The most common external metrics are tests of the system’s functions, reliability, and performance. Measuring Quality Attributes (Cont’d)  Quality metrics should be specified as unambiguously as possible.  Qualities may be specified with scenarios specified by the software designers and architects with assistance form the acquirers and users. Quality Requirements and Architectural Design  Quality measurements are performed primarily on the architectural description.  While some measurements are quantitative, most are qualitative.  Qualitative evaluations, while not as rigorous as quantitative evaluations, can be objective and provide useful predictions about he success of the system in meeting quality requirements. Quality Requirements and Architectural Design (Cont’d)  Quality attributes can be addressed through architectural styles and patterns.  Different architectural styles address different sets of quality attributes and to varying degrees.  The specification of quality attributes, therefore affects the architectural style of the system. Quality Requirements and Architectural Design (Cont’d)  Not all quality attributes are addressed by the architectural design.  Usability and performance both have nonarchitectural aspects. Systems Knowledge and Quality Attributes  In terms of levels of systems knowledge, the identification of quality attributes is equivalent to the source level (level 0) of systems knowledge.  Quality requirements are specific values or ranges of values for these attributes which is data level knowledge about the system (level 1). Systems Knowledge and Quality Attributes (Cont’d)  Software architecting begins with creating models (generative level of systems knowledge, or level 2) that can generate the data level knowledge.  We evaluate the architecture to see if it indeed produces the same data as specified in level 1. Barriers to Achieving Quality  Common reasons for failure to meet high levels of quality include:    Misunderstanding of the importance of quality attributes Inadequate languages for expressing and specifying quality requirements Inadequate modeling methods and notations for expressing solutions that address specific quality attributes Barriers to Achieving Quality (Cont’d)  Common reasons for failure to meet high levels of quality include (cont’d):    Difficulty in designing for quality attributes Lack of documented design and architecture patterns for addressing quality attributes Quality control as an afterthought in most projects Common Quality Attribute Misunderstandings  Specifying Quality Requirements  There has been little work in the field of formal specification for nonfunctional requirements  Modeling Methods Don’t Address Quality Attributes  Design methodologies are weak in representing nonfunctional requirements  Designing for Quality Attributes  Quality attributes are interdependent and cannot be achieved in isolation Common Quality Attribute Misunderstandings (Cont’d)  Solution Catalogues and Quality Attributes   Design patterns can be used to address some quality attributes, but mapping them to a design pattern’s context and problem statements is not easy. It may be worthwhile to begin cataloguing patterns with respect to standardized quality attributes  Quality Control is an Afterthought  Putting testing off until the end of the project is effectively a statement that quality is not important enough to be assessed early Understanding Quality Models  A quality model is a specification of the required characteristics that a software system must exhibit.  Several quality models have been developed over the years.  McCall/GE Quality Model  Organizes quality around three uses of software: product revision, product operations, and product transition Understanding Quality Models (Cont’d)  Several quality models have been developed over the years. (Cont’d)  Boehm Quality Model  Shares a common subset with the McCall model and identifies additional quality attributes  ISO/IEC 9126-1:2001 Quality Standard  Identifies six quality characteristics – functionality, reliability, usability, efficiency, maintainability, and portability. These are further divided into several subcharacteristics Understanding Quality Models (Cont’d)  Recent work at the SEI at CMU has produced a framework for specifying quality models by adding more precision to quality attribute definitions and introducing metrics and analysis techniques for measuring software and architecture descriptions.  Most development organizations do not employ formal metrics for nonfunctional requirements. They rely on testing, inspections and subjective assessments of quality.  If done right, these methods can be an effective way of predicting system quality. Quality Metamodel Observable Via Execution Not Observable Via Execution External Characteristic 1 1…* manifestation of Internal Quality Attribute name value 1 addresses 1…* 1…* Engineering Practice measure 1…* Metric scale method Scenario Architecting Practice

Quality Models and Quality Attributes, Part 1

Related Documents

Recommended Documents

Description

Related Documents

Free up your schedule!

Take 5 seconds to unlock