What is a context diagram

System delimitation


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Delimitation of the examination area using a context diagram

The delimitation of the investigation area is extremely important for a project in systems analysis. Nevertheless, it is often used too late and improperly in the practice of requirements analysis. For example, in information engineering, the System context only defined in the analysis phase (see also software engineering process models).
With an early implementation during the system planning, the following aspects can be clarified as essential facts via the system delimitation in a black box and visualized via a diagram (context diagram as ⇓information flow diagram⇓ or UML diagram⇓):

  • Which components belong to the project and which are outside,
  • that the project goals match the project content,
  • that all those responsible for the components of the system interfaces are involved in the planning and
  • that the necessary competence is accordingly available in the project.

The clarification of these questions facilitate the tasks in project management or the project manager. It should also be determined whether the diagram represents the system context or, as a project delimitation, the project context as a section of the system.

In the system delimitation the path leads to a context diagram

  1. Analysis of external partners (stakeholder analysis)
    Who is the system developed for?
    Who can facilitate the performance of their tasks by using the system?
    Who is the recipient or supplier of services?
    Who has an information requirement that the IT system can cover?
    Who is entrusted with the administration and maintenance of the system?
    Requirement for means analysis and communication flow analysis.

  2. Impact analysis
    What should the system produce? (Requirements catalog!)
    Which effects influence the system?
    Which services can be outsourced to separate IT systems? (Goal: projects with a smaller scope!)

  3. Means analysis
    How does the material flow between external partners (e.g. customer, supplier) and the system look like? (Material flow can include goods or money, for example.)

  4. Communication flow analysis
    Communication flow between external partners and the system.
    Which functions can be used to better coordinate tasks between external partners?
    What information do external partners have to provide so that the system can perform its tasks?
    How must the system interfaces to other applications / information systems be designed?

  5. Influencing variable analysis
    Type and extent of external influences on a system (roles - interests - influences).
    Who has to be involved in the project planning?
    In the influencing variable analysis, the effect of external influences on the system is assessed.

external links

In some cases, the stakeholder analysis produces comparable results. The focus here is on the influences on the project as well as the relationships between the stakeholders.

The system delimitation is shown graphically in the context diagram as Information flow diagram (Data flow diagram) with the elements

  • function (Process, task),

  • External partner (Participant, External Interface, Terminator) and

  • flow of information (Communication flow, data flow, material flow, control flow)

shown. In addition, a definition and description is created for all elements contained in the context diagram. The aim of the description is to increase the precision of the delimitation.

In structured analysis, the context diagram is referred to as a level 0 data flow diagram.

Wikipedia: Stakeholder analysis as part of the environmental analysis

Example: Modeling context diagram to delimit the "system: accommodation" in a hotel business as Information flow diagram (IFD)

The customer and guest are external participants in the context diagram,
Marketing as an in-house department is also an external partner of the "accommodation" system,
In the example, financial accounting, procurement and managing partners are by definition independent hotel systems with interfaces for accommodation.
The external partners / external interfaces together represent the environment of the "Manage accommodation" application in the context diagram and are each connected to the system via an information flow / communication flow / data flow.

The system delimitation can also be in the notation of the Unified Modeling Language as UML context diagram being represented.

Example: UML context diagram with the objects actor and use case for the application "Manage accommodation"

In the requirements analysis, the Use case diagram however, usually sections of the IT system for related use cases or business processes (see also business process modeling) are shown. This means that the representation of a system delimitation in UML modeling is usually only feasible by defining several use case diagrams. The definition of the content of the interface between the external partners and the system is also not visible in the diagram.

In the UML modeling procedure, the term context diagram is also used to represent the environment of an individual object and to derive the requirements from it. All objects with which a selected object is related are then shown in the diagram.

Offers on the topic of delimitation of the examination area within the framework of the system analysis INffORUM Training (seminar, workshop, tutorial) and in project work coaching and support in project implementation. The use of tools, both for SA tools and for UML tools, can also be taught in the training (see also Tools Software Engineering).

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As of May 3, 2018

The training on the method of system delimitation, seminar as well as workshop and tutorial, can be tailored to the specific needs of a project group. The implementation is mostly related to other methods of requirements analysis or application development.

Benefit from the many years of experience in your IT project INffORUM Consultant.