Suitability Attributes of software that bear on the presence and appropriateness of a set of functions for specified tasks. Attributes of software that bear on the provision of right or agreed results or effects. Functionality Attributes of software that bear on its ability to interact with specified systems. Compliance Attributes of software that make the software adhere to application related standards or conventions or regulations in laws and similar prescriptions.
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Maintainability Portability These characteristics are broken down into subcharacteristics, a high level table is shown below. It is at the subcharacteristic level that measurement for SPI will occur. The main characteristics of the ISO quality model, can be defined as follows:- Functionality Functionality is the essential purpose of any product or service. The more functions a product has, e. For software a list of functions can be specified, i. A sales order system should also provide the following functions: Record sales order product, price and quantity.
Calculate total price. 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. Many people get confused between overall process functionality in which software plays a part 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. The relationship between software functionality within an overall business process is outside the scope of ISO and it is only the software functionality, or essential purpose of the software component, that is of interest for ISO Following functionality, there are 5 other software attributes that characterize the usefulness of the software in a given environment.
Each of the following characteristics can only be measured and are assumed to exist when the functionality of a given system is present. Reliability Once a software system is functioning, as specified, and delivered the reliability characteristic defines the capability of the system to maintain its service provision under defined conditions for defined periods of time.
One aspect of this characteristic is fault tolerance that is the ability of a system to withstand component failure. For example if the network goes down for 20 seconds then comes back the system should be able to recover and continue functioning. Usability Usability only exists with regard to functionality and refers to the ease of use for a given function.
For example a function of an ATM machine is to dispense cash as requested. Placing common amounts on the screen for selection, i. The ability to learn how to use a system learnability is also a major subcharacteristic of usability. Efficiency This characteristic is concerned with the system resources used when providing the required functionality. The amount of disk space, memory, network etc. As with a number of these characteristics, there are overlaps.
Maintainability The ability to identify and fix a fault within a software component is what the maintainability characteristic addresses.
In other software quality models this characteristic is referenced as supportability. Maintainability is impacted by code readability or complexity as well as modularization.
Anything that helps with identifying the cause of a fault and then fixing the fault is the concern of maintainability. Also the ability to verify or test a system, i. Portability This characteristic refers to how well the software can adopt to changes in its environment or with its requirements. The subcharacteristics of this characteristic include adaptability.
Object oriented design and implementation practices can contribute to the extent to which this characteristic is present in a given system.
ISO 9126: The Standard of Reference