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SNAP Points
SNAP is the acronym for "Software Non-functional Assessment Process," a measurement of the size of non-functional software. The SNAP sizing method complements ISO/IEC 20926:2009, which defines a method for the sizing of functional software. SNAP is a product of the International Function Point Users Group (IFPUG), and is sized using the “Software Non-functional Assessment Process (SNAP) Assessment Practices Manual” (APM) now in version 2.4. Reference “IEEE 2430-2019-IEEE Trial-Use Standard for Non-Functional Sizing Measurements,” published October 19, 2019 ([1]). Also reference ISO standard “Software engineering — Trial use standard for software non-functional sizing measurements,” (https://www.iso.org/standard/81913.html), published October 2021. More information about SNAP can be found by going to YouTube and searching for "IFPUG SNAP;" which will provide a series of videos overviewing the SNAP methodology.
A software application can provide two aspects of value to its users. In this context, the first aspect is "what" the software will do, specifically, "A subset of the user requirements. Requirements that describe what the software shall do, in terms of tasks and services." (ISO/IEC 14143-1 definition) This can be defined as its "functionality." One metric used to measure the size of one unit of this functional software is the “function point.” By using an ISO-standard functional sizing metric (FSM) such as that in the IFPUG “Function Point Counting Practices Manual,” (FSM ISO/IEC 20926:2009), a function point counting specialist can examine the software application's functional user requirement portion and measure its functional size in units of function points.
For more detail on the function point metric, and other organizations’ functional software sizing metrics, see the bibliography, the Wikipedia article “function point,” and numerous references in the literature.
A software user requirement also may specify "how" the software will do it, specifically "A software requirement that describes not what the software will do but how the software will do it." (ISO/IEC/IEEE 24765:2010 definition) These types of software are defined by IFPUG as being “non-functional.” The corresponding software size is measured by SNAP. The IFPUG APM details how to size the application's non-functional software. The non-functional aspects are defined and classified in ISO/IEC 25010:2011, “Systems and software engineering -- Systems and software Quality Requirements and Evaluation (SQuaRE) -- System and software quality models”.
The functional size of the software, together with the non-functional size of the software, should be used for measuring the total software size of software projects. The two sizes should be used to measure the performance of the software project, setting benchmarks, and estimating the cost and duration of software projects.
Similar to function point sizing, one unit of non-functionality is the “SNAP point.” The size of the software derived by quantifying the non-functional portion of an application can be measured by using the procedure in the APM. Similar to function points, by using the IFPUG APM, a SNAP point counting specialist can examine the software application and measure the size of its non-functionality in units of SNAP points. Also like function points, the number of SNAP points in an application correlates with the work effort to develop the non-functional software portion of that application. The original research detailing this correlation is in CrossTalk The Journal of Defense Software Engineering, as the paper “A New Software Metric to Complement Function Points The Software Non-functional Assessment Process (SNAP).”
Each aspect of software (the functional and the non-functional) requires work effort to develop, which is proportional to their sizes. Software development organizations can use their correlations between function points and their work effort, and between SNAP points and their work effort, to help forecast their software development costs and schedules and to audit projects to determine how well funding was spent and schedules were managed
SNAP recognizes four categories and 14 subcategories of non-functional user requirements. These are in the below table from the APM.
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SNAP Points
SNAP is the acronym for "Software Non-functional Assessment Process," a measurement of the size of non-functional software. The SNAP sizing method complements ISO/IEC 20926:2009, which defines a method for the sizing of functional software. SNAP is a product of the International Function Point Users Group (IFPUG), and is sized using the “Software Non-functional Assessment Process (SNAP) Assessment Practices Manual” (APM) now in version 2.4. Reference “IEEE 2430-2019-IEEE Trial-Use Standard for Non-Functional Sizing Measurements,” published October 19, 2019 ([1]). Also reference ISO standard “Software engineering — Trial use standard for software non-functional sizing measurements,” (https://www.iso.org/standard/81913.html), published October 2021. More information about SNAP can be found by going to YouTube and searching for "IFPUG SNAP;" which will provide a series of videos overviewing the SNAP methodology.
A software application can provide two aspects of value to its users. In this context, the first aspect is "what" the software will do, specifically, "A subset of the user requirements. Requirements that describe what the software shall do, in terms of tasks and services." (ISO/IEC 14143-1 definition) This can be defined as its "functionality." One metric used to measure the size of one unit of this functional software is the “function point.” By using an ISO-standard functional sizing metric (FSM) such as that in the IFPUG “Function Point Counting Practices Manual,” (FSM ISO/IEC 20926:2009), a function point counting specialist can examine the software application's functional user requirement portion and measure its functional size in units of function points.
For more detail on the function point metric, and other organizations’ functional software sizing metrics, see the bibliography, the Wikipedia article “function point,” and numerous references in the literature.
A software user requirement also may specify "how" the software will do it, specifically "A software requirement that describes not what the software will do but how the software will do it." (ISO/IEC/IEEE 24765:2010 definition) These types of software are defined by IFPUG as being “non-functional.” The corresponding software size is measured by SNAP. The IFPUG APM details how to size the application's non-functional software. The non-functional aspects are defined and classified in ISO/IEC 25010:2011, “Systems and software engineering -- Systems and software Quality Requirements and Evaluation (SQuaRE) -- System and software quality models”.
The functional size of the software, together with the non-functional size of the software, should be used for measuring the total software size of software projects. The two sizes should be used to measure the performance of the software project, setting benchmarks, and estimating the cost and duration of software projects.
Similar to function point sizing, one unit of non-functionality is the “SNAP point.” The size of the software derived by quantifying the non-functional portion of an application can be measured by using the procedure in the APM. Similar to function points, by using the IFPUG APM, a SNAP point counting specialist can examine the software application and measure the size of its non-functionality in units of SNAP points. Also like function points, the number of SNAP points in an application correlates with the work effort to develop the non-functional software portion of that application. The original research detailing this correlation is in CrossTalk The Journal of Defense Software Engineering, as the paper “A New Software Metric to Complement Function Points The Software Non-functional Assessment Process (SNAP).”
Each aspect of software (the functional and the non-functional) requires work effort to develop, which is proportional to their sizes. Software development organizations can use their correlations between function points and their work effort, and between SNAP points and their work effort, to help forecast their software development costs and schedules and to audit projects to determine how well funding was spent and schedules were managed
SNAP recognizes four categories and 14 subcategories of non-functional user requirements. These are in the below table from the APM.