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Context and Scope

Contents

Context and scope - as the name suggests - delimits your system (i.e. your scope) from all its communication partners (neighboring systems and users, i.e. the context of your system). It thereby specifies the external interfaces.

If necessary, differentiate the business context (domain specific inputs and outputs) from the technical context (channels, protocols, hardware).

Motivation

The domain interfaces and technical interfaces to communication partners are among your system's most critical aspects. Make sure that you completely understand them.

Form

Various options:

  • Context diagrams

  • Lists of communication partners and their interfaces.

See Context and Scope in the arc42 documentation.

Business Context

Contents

Specification of all communication partners (users, IT-systems, ...) with explanations of domain specific inputs and outputs or interfaces. Optionally you can add domain specific formats or communication protocols.

Motivation

All stakeholders should understand which data are exchanged with the environment of the system.

Form

All kinds of diagrams that show the system as a black box and specify the domain interfaces to communication partners.

Alternatively (or additionally) you can use a table. The title of the table is the name of your system, the three columns contain the name of the communication partner, the inputs, and the outputs.

Diagram or Table

C4Context
title System Context diagram for Internet Banking System
Enterprise_Boundary(b0, "BankBoundary0") {
Person(customerA, "Banking Customer A", "A customer of the bank, with personal bank accounts.")
Person(customerB, "Banking Customer B")
Person_Ext(customerC, "Banking Customer C", "desc")

Person(customerD, "Banking Customer D", "A customer of the bank, <br/> with personal bank accounts.")

System(SystemAA, "Internet Banking System", "Allows customers to view information about their bank accounts, and make payments.")

Enterprise_Boundary(b1, "BankBoundary") {

    SystemDb_Ext(SystemE, "Mainframe Banking System", "Stores all of the core banking information about customers, accounts, transactions, etc.")

    System_Boundary(b2, "BankBoundary2") {
    System(SystemA, "Banking System A")
    System(SystemB, "Banking System B", "A system of the bank, with personal bank accounts. next line.")
    }

    System_Ext(SystemC, "E-mail system", "The internal Microsoft Exchange e-mail system.")
    SystemDb(SystemD, "Banking System D Database", "A system of the bank, with personal bank accounts.")

    Boundary(b3, "BankBoundary3", "boundary") {
    SystemQueue(SystemF, "Banking System F Queue", "A system of the bank.")
    SystemQueue_Ext(SystemG, "Banking System G Queue", "A system of the bank, with personal bank accounts.")
    }
}
}

BiRel(customerA, SystemAA, "Uses")
BiRel(SystemAA, SystemE, "Uses")
Rel(SystemAA, SystemC, "Sends e-mails", "SMTP")
Rel(SystemC, customerA, "Sends e-mails to")

UpdateElementStyle(customerA, $fontColor="red", $bgColor="grey", $borderColor="red")
UpdateRelStyle(customerA, SystemAA, $textColor="blue", $lineColor="blue", $offsetX="5")
UpdateRelStyle(SystemAA, SystemE, $textColor="blue", $lineColor="blue", $offsetY="-10")
UpdateRelStyle(SystemAA, SystemC, $textColor="blue", $lineColor="blue", $offsetY="-40", $offsetX="-50")
UpdateRelStyle(SystemC, customerA, $textColor="red", $lineColor="red", $offsetX="-50", $offsetY="20")

UpdateLayoutConfig($c4ShapeInRow="3", $c4BoundaryInRow="1")

Optionally: Explanation of external domain interfaces

Technical Context

Contents

Technical interfaces (channels and transmission media) linking your system to its environment. In addition a mapping of domain specific input/output to the channels, i.e. an explanation which I/O uses which channel.

Motivation

Many stakeholders make architectural decision based on the technical interfaces between the system and its context. Especially infrastructure or hardware designers decide these technical interfaces.

Form

E.g. UML deployment diagram describing channels to neighboring systems, together with a mapping table showing the relationships between channels and input/output.

<Diagram or Table

<optionally: Explanation of technical interfaces

<Mapping Input/Output to Channels