Context and Data Flow Diagrams Ms Sanchez Context

Context and Data Flow Diagrams n The main tools used to pictorially depict how

Context and Data Flow Symbols n There are 4 symbols in these types of

Data flows n Data flows describe the data being transferred. NOT THE PROCESSING! n

Process or System n The circle represents the whole information processing system or a

Entity n People, programs, organisations or other IS that provide data to the system

Data Storage n Type of storage is irrelevant. n The name of the data

Context Diagrams n A context diagram is the highest level of the data flow

Context Diagram Example Booking Diners Bill Orders Nishan’s Restaurant System Invoice Food Suppliers Food

Drawing DFDs Creating Logical DFDs • logical DFD of the same processing customer order

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Context and Data Flow Diagrams Ms Sanchez

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

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

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

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

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

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

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

Context Diagram Example Booking Diners Bill Orders Nishan’s Restaurant System Invoice Food Suppliers Food Orders

Drawing DFDs Creating Logical DFDs • logical DFD of the same processing customer order 2. 1 checked check customer order accepted order 2. 3 commit resources 2. 2 Check production feasibility order details resources used resources schedule