Context and Data Flow Diagrams Ms Sanchez

Context and Data Flow Diagrams The main tools used to pictorially depict how application data and information moves through the system. The processes that manipulate the data and produce information are named but not fully described.

Context and Data Flow Symbols There are 4 symbols in these types of diagrams. Entity Process or System Data store Data flow

Data flows Data flows describe the data being transferred. NOT THE PROCESSING! Uses nouns (naming words) to name data flows.

Process or System The circle represents the whole information processing system or a specific process in the system. Verbs (actions words) are used to name processes Nouns (naming words) are used for information systems to indicate their purpose.

Entity People, programs, organisations or other IS that provide data to the system or receive output from the system are external entities. They are also called: “source” or “destination of data”. Nouns (naming words) are used to name external entity types

Data Store Type of storage is irrelevant. The name of the data store is placed between the lines and identifies the data it holds. Nouns are used to name data stores. A data store represents a set of data records that are unique but have similar characteristics.

Context Diagrams A context diagram is the highest level of the data flow diagram. It gives a general description of the system. Indicates the relationship between the system and the rest of the world. CDs identify and document all the data that flows into and out of the system. It doesn’t show much detail

Context Diagram Example Bookin g Nishan’s Restaurant System Invoic e Food Suppliers Diners Bill Orders Food Orders

Drawing DFDs Creating Logical DFDs logical DFD of the same processing 2.1 checked customer order 2.2 customer order check customer order Check production feasibility accepted order order details 2.3 order commit resources resources used resources schedule