The following figure shows an overview of a requirements structure including
all of its elements defined below.
[ fig. rmt_e_a04_01 ]
The base requirement represents the top node of a requirements structure (see fig. rmt_e_a04_01 ).
The person who pays for the development of the product (see also Customer).
A person who pays the product (see also Client).
An external requirement directly originates from a need stated by units outside systems engineering such as the customer or a marketing department. External requirements usually become part of the contractual obligations towards the customer (see fig. rmt_e_a04_01 ).
A formalized requirement (synonym: Parameter) represents a requirement statement transformed into a computer-processable format. Formalized requirements are attached to text requirements (see fig. rmt_e_a04_01 ). One text requirement may have one or more formalized requirements linked to it.
Internal requirements are complementary to external requirements (see fig. rmt_e_a04_01 ). Internal requirements usually do not become part of the contractual obligations towards the customer. They are defined to fully specify the expected properties and behavior of the product throughout the entire product life cycle not only from the customer's point of view, but also from the company-internal point of view. A requirements structure containing both external and internal requirements is often called 'specification tree'.
Non-requirement text is meant to provide background or contextual information on various text requirement. Unlike an explanation given for a single requirement only, non-requirement text can be linked to more than one requirement.
see 'Formalized Requirement' (> Formalized Requirement)
By means of a requirements analysis activity the generation of new requirements based on yet existing ones (see 'Requirements Derivation') can be supported and documented.
Similar to a configuration baseline the requirement baseline defines something like the staring point in the process of tracking and control of requirements and the product which has to fulfill these requirements. You can understand the set of all specifications with their first released edition –representing the functional structure of a product or system- as the requirement baseline.
During decomposition a text requirement is broken down into two or more text requirements whose total content is equal to the content of the former requirement - just expressed in more detail, i.e. at a higher level or granularity). The decomposed requirement is replaced by the resulting requirements, therefore becomes 'obsolete', but remains in the system.
Deriving requirements means creating new requirements based on one or more yet existing ones. Unlike for requirement decomposition (> Requirement Decomposition), the statements of the newly created requirements are different from those of the existing ones. Consequently, the input requirements do not become obsolete. If desired the derivation may be documented by means of a Requirements Analysis Activity (> Requirements Analysis Activity).
Requirements sets contain two or more text requirements (> Text Requirement) interrelated to each other according to a certain aspect. This aspect may be a temporal or logical constraint, an equation an alternative etc. Requirement sets may furthermore be used to bundle redundant or conflicting text requirements.
A document that contains the requirements and defines the product.
A requirement statement represents a single requirement issue in textual form. A text requirement contains one or more requirement statements. A requirement statement may be formalized and thus transformed into a computer-processable format (see > Formalized Requirement).
A product- or project-specific, hierarchical representation of base, structure and text requirements as well as the relations between them.
See Requirements Structure.
On the one hand structure requirements group other structure or text requirements at the inferior levels of the requirement structure and on the other hand establish links to further structure requirements or the base requirement at the superior levels of the requirements structure (see fig. rmt_e_a04_01 ).
A text requirement (see fig. rmt_e_a04_01 ) describes in textual form the needs, demands and constraints with respect to the properties and behavior of the future product in any phase of its life cycle. A text requirement contains one or more requirement statements (> Requirement Statement).
Traceability is the ability to identify
An amount of work as seen from the viewpoint of the user of the product [RoR 99].