5.6 Category of Methods "Estimation Models" (EMOD)
SMOD - Schätzmodelle
In the Methods Standard, method Review
For the effort estimation required within the scope of the preliminary and detailed planning of the Project Management, the category of methods Estimation Models is defined in the Methods Standard. An individual method, a definite estimation procedure as e. g. the Function Point Method or CoCoMo is only selected within the scope of the operationalization of the Methods Standard.
It is not possible to specify a definite procedure already within the Methods Standard. Nevertheless, in spite of the large number of estimation procedures exists none that might be suggested as the "standard method". Each one of the procedures has certain faults. Besides, the selection of a procedure is influenced by a variety of marginal conditions and factors. In addition the Methods Standard should be open to new developments at this point.
Primarily, the category of methods Estimation Models comprises all procedures applicable for the effort estimation. Even if-in accordance with the appraisal criteria mentioned below-a procedure is basically suited for the application in the V-Model, it cannot as a rule be universally applied since effort estimation is particularly dependent on and influenced by external factors, such as the organizational and project-specific environment. Therefore, the operation criteria must be defined for each basically applicable estimation procedure.
In this connection, the appraisal criteria are constant values referring to the estimation procedure itself. The operation criteria are variable values referring to the individual project-specific environment and are thus different in every project. Only after the results from the two investigation steps is it possible to select a certain estimation procedure for an actual project environment. And even then an adjustment to the software development process according to the V-Model is required for most of the remaining methods, provided they are not only supporting a macro estimation.
Next, the criteria are listed that can be used to appraise the basic suitability and usability of an estimation method in the V-Model/Project Management. The listed appraisal criteria should be used as a measuring device, in particular for new developments in this field.
There exists hardly any estimation method able to meet all these criteria (it also contains some "desired criteria", in particular the last three items); in order to be classified as suitable for the application in the V-Model, though, the predominant part should be evaluated as positive.
Next, the criteria are listed that are used to define the application field for an estimation method since not all estimation methods are equally suited for each individual application.
- The estimation method supplies values, both for the macro (total effort) and for the micro estimation (effort for the individual submodels SD, QA, CM, PM, the individual SD (sub-) activities, and the individual functional units).
- The estimation method does not-or not only-use LOC (lines of code) as a basis for the estimation; the quantity of the software or respectively the size of the project is evaluated on the basis of several measuring quantities that can directly be allocated to the corresponding activity.
- The estimation method attempts to be as objective as possible, i. e. by integrating factors able to quantify and its determination, based on exact definitions.
- The estimation method takes into consideration independent project, product, personnel, and technology parameters that can be evaluated.
- The estimation method itself is comprehensible, stable and reliable.
- The estimation method supports the deviation of a cost and time estimation from the calculated effort by taking into consideration the project- and company-oriented marginal conditions.
- Tools available on the market support the user of the estimation method when determining the required parameters, calculating the estimated values, and setting up an experience database.
- The estimation method successively integrates the actual values according to the project progress into the estimation.
- The estimation method is based on a SW life cycle comparable with the V-Model or else uses a life cycle transformed to or transformable to the V-Model lifecycle.
- Just like the V-Model, the estimation method takes into consideration a tailoring process, i. e. in case certain activities or products in the development process are not required this fact is utilized for the effort estimation.
It is not possible to list all existing individual methods in this documentation. However, each estimation method can be traced to one or to a combination of basic types. According to /Noth, 86/, the basic types are:
- Suitability for a certain system type
is given, e. g., if the influence factors taken into consideration are predominantly typical of a technical or commercial software development.
- Suitability for a certain project type
is given, e. g., if the estimation method only uses measuring quantities and influence factors applicable to a new development and not, however, to SWMM.
- Suitability for a certain project size
is given, e. g., if based on empirical studies it was ascertained that realistic estimation values could only be obtained within a certain range.
- Suitability for a certain development and target environment
is given, e. g., if the estimation basis LOC and the corresponding productivity refer to a certain programming language or if the measuring quantities require a certain methodical procedure.
The two best known and-based on its versions and further developments-most frequently applied individual methods for the effort estimation are
which are introduced next. Many of the effort estimation methods presented in literature and implemented in tools use one of these two approaches.
Apart from that, also the less known method
- analog method
- relation method
- multiplier method
- weighting method
- method of parametric estimation equations
- percentage method
is considered as relevant; the utilization of an experience database is the core of this method and therefore permits interesting perspectives.
188.8.131.52 Function Point Method (FPM)
- Integrated Procedure for the Effort Estimation (INVAS)(1)
184.108.40.206 Constructive Cost Model (CoCoMo)
(1) INVAS /Noth, 1986/ was developed within the scope of a research project of Cologne University in cooperation with Siemens AG. INVAS is no completely defined method. It rather suggests a procedure which has to be specified in various ways for various development environments.
INVAS separates the effort estimation into a quantity and into a productivity estimation. In this connection, the project is structured into subproducts and milestone results. These are evaluated according to their qualitative influence factors (e. g. system size, processing mode, degree of innovation, experience, technology) and special measuring quantities (e. g. requirements, functions, program lines, documentation pages, interfaces, test cases). After that the productivity based on the values stored in an experience database can be estimated. In this connection, subproducts with similar influence factors and measuring are utilized.
Last Updated 01.Jan.2002
Updated by Webmaster
Last Revised 01.Jan.2002
Revised by Webmaster