Page 267 - DCAP304_DCAP515_SOFTWARE_PROJECT_MANAGEMENT

Unit 13: Software Quality

ISO 9126-1 symbolizes the latest research into characterizing software for the purposes of software Notes
quality control, software quality assurance and software process improvement (SPI). The ISO
9126-1 software quality model recognizes 6 main quality characteristics:
 Functionality
 Reliability

 Usability
 Efficiency
 Maintainability
 Portability
These characteristics are broken down into sub characteristics; a high level table is shown
below. It is at the sub characteristic level that measurement for SPI will occur. The main
characteristics of the ISO9126-1 quality model can be defined as follows:-

Functionality

Functionality is the essential purpose of any product or service. For certain items this is relatively
easy to define, for example a ship’s anchor has the function of holding a ship at a given location.
The more functions a product has, e.g. an ATM machine, then the more complicated it becomes
to define it’s functionality. For software a list of functions can be specified, i.e. a sales order
processing systems should be able to record customer information so that it can be used to
reference a sales order.

Did u know? What is sales order system?
A sales order system should also provide the following functions:
 Record sales order product, price and quantity.

 Calculate total price.
 Calculate appropriate sales tax.
 Calculate date available to ship, based on inventory.
 Generate purchase orders when stock falls below a given threshold.

The list goes on and on but the main point to note is that functionality is expressed as a totality
of essential functions that the software product provides. It is also important to note that the
presence or absence of these functions in a software product can be verified as either existing or
not, in that it is a Boolean (either a yes or no answer). The other software characteristics listed
(i.e. usability) are only present to some degree, i.e. not a simple on or off. Many people get
confused between overall process functionality (in which software plays a part) and software
functionality. This is partly due to the fact that Data Flow Diagrams (DFDs) and other modeling
tools can depict process functionality (as a set of data in\data out conversions) and software
functionality. Consider a sales order process, that has both manual and software components. A
function of the sales order process could be to record the sales order but we could implement
a hard copy filing cabinet for the actual orders and only use software for calculating the price,
tax and ship date. In this way the functionality of the software is limited to those calculation
functions. SPI, or Software Process Improvement is different from overall Process Improvement
or Process Re-engineering, ISO 9126-1 and other software quality models do not help measure
overall Process costs/benefits but only the software component. The relationship between

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