External Entity

• External entities are people, places, or things which interact with the application. 
• Usually, we identify titles/roles (e.g.,  Customer), departments (e.g., Accounts Receivable), organizations (e.g., Medicare Administration), or applications (e.g.,  Accounts Receivable Application) as entities. 
• The phrase 'interact with the application'  has a very specific meaning.  
• The entity is  outside the control and/or processing being modeled for the  current application.  That is,  external entity processing, procedures, and data are not subject to analysis or change. 
• Relationships between external entities are  not shown on the diagram(s) (i.e., external entities cannot connect to  each other).
• if you are modeling an  order processing application that does not do inventory control, the warehouse would be on the context diagram.  
• If inventory  control  and  warehouse  processing  are within the scope of the application, the warehouse would not be on the context diagram

Dictionary of External Entity

• Entity Name
• Aliases
• Definition
• Relationship to Application
• Contact, if entity is an organization

Sumber: Conger, 2008

Contex Diagram

Introduction:

• A context diagram depicts the scope of the project, using circles, squares, and arrows.  
• A large circle  designates  the  application. 
• Squares  identify external entities  with  which  the application must interact.  
• Directed lines are the data flows  which indicate movement of data between entities and the application.

Rules:

• Define the boundaries (i.e.,  scope) of the application. Specifically, define what the application will do and what it will not do.  Draw the circle identifying the application and write the application name in the center. 
• Using the application boundary as  a starting point, identify all external entities with which the application must interact. For each entity, draw one square on the diagram and label the square. 
• For each entity, create a definition in the data dictionary. 
• For each external entity, identify the specific data flows  that define the interface. 
• For each data flow,  create a definition and list of tentative contents in the data dictionary. 
• For a complex application, you might need two levels of context  diagrams.  
• One level  summarizes all entities with directed arrows  that are unlabeled. 
• The other level shows input flows  on one diagram, and output flows  on the other diagram with labeled data flows  on both diagrams.

Sumber: Conger, 2008