System Analysis and Design Data Flow Diagram

Data Flow diagram The dataflow diagram is a modeling tool that allows us to picture a system as a network of functional processes, connected to one another by “pipelines” and “holding tanks” of data

Data Flow Diagrams Context Diagrams Top-level view of an information system that shows the system’s boundaries and scope Do not show any data stores in a context diagram because data stores are internal to the system. Begin by reviewing the system requirements to identify all external data sources and destinations

Context Diagrams Record the name of the entities and the name and content of the data flows, and the direction of the data flows. What makes one system more complex than another is the number of components, the number of levels, and the degree of interaction among its processes, entities, data stores, and data flows

Context Diagrams Shows the overall business process as just one process. The process is given the number zero. Shows all the outside entities that receive information from or contribute information to the system

Context Diagrams Each context diagram must fit on one page. The process name in the context diagram should be the name of the information system. Use unique names within each set of symbols. Do not cross lines. Use a unique reference number for each process symbol.

Developing DFDs 1. Context Diagram for Pizza Hut food ordering system CUSTOMER KITCHEN Food Order Customer Order Receipt Management Reports RESTAURANT MANAGER

Creating a Set of DFDs Create a graphical model of the information system based on your fact-finding results Performing three main tasks Step 1: Draw a context diagram Step 2: Draw a diagram 0 DFD Step 3: Draw the lower-level diagrams

Creating a Set of DFDs Draw a Diagram 0 DFD Diagram 0 Zooms in on the context diagram and shows major processes, data flows, and data stores Must retain all the connections that flow into and out of process 0 Each process has a reference number Diverging data flow

Draw the Lower-Level Diagrams Creating a Set of DFDs Draw the Lower-Level Diagrams Must use leveling and balancing techniques Leveling Uses a series of increasingly detailed DFDs to describe an information system Exploding, partitioning, or decomposing

Data Flow Diagrams Lower-Level Diagrams Balancing Ensures that the input and output data flows of the parent DFD are maintained on the child DFD

Developing DFDs 1. Context Diagram for Pizza Hut food ordering system CUSTOMER KITCHEN Food Order Customer Order Receipt Management Reports RESTAURANT MANAGER

Developing DFDs 2. Level-0 Diagram for Pizza Hut food ordering system 1.0 Receive & Transform Customer Food Order CUSTOMER KITCHEN Customer Order Food Order Receipt 2.0 Update Goods Sold File 3.0 Update Inventory File Inventory Data Goods Sold Formatted Goods Sold Data Formatted Inventory Data D2 D1 Goods Sold File Inventory File 4.0 Produce Management Report Daily Inventory Depletion Amounts Daily Goods Sold Amounts manager Management Reports

Developing DFDs 2. Level-1 Diagram for Pizza Hut food ordering system 1.1 Receive Customer Order 1.3 Transform Order to Kitchen Format Customer Order Customer Order Food Order Customer Order 1.5 Generate Inventory Decrements Customer Order Inventory Data Customer Order 1.2 Generate Customer Receipt 1.4 Generate Goods Sold Increments Receipt Goods Sold Data

Rules Governing Data Flow Diagramming

Rules Governing Data Flow Diagramming Process Process cannot have outputs only. It means it is making data from nothing Only a source should have outputs without inputs

Rules Governing Data Flow Diagramming Process No Process can have only inputs If an object has only inputs, then it must be a sink.

Rules Governing Data Flow Diagramming Process A Process should have a verb phrase label Generate Orders

Rules Governing Data Flow Diagramming Process Data cannot move directly from one data store to another data store. Data must be moved by a process Generate Orders

Rules Governing Data Flow Diagramming Process Data cannot move directly from an outside source to a data store Data must be moved by a process which receives data from the source and places the data into the data store Generate Orders Source Source

Rules Governing Data Flow Diagramming Process Data cannot move directly to an outside sink from a data store Data must be moved by a process Generate Orders Sink Sink

Rules Governing Data Flow Diagramming Process A data store has a noun phrase label Inventory

Rules Governing Data Flow Diagramming Process A data store A data store must have at least one incoming and one outgoing data flow. Inventory

Rules Governing Data Flow Diagramming Process Source/Sink Rule 9: Data cannot move directly from a source to a sink It must be moved by a process Generate Orders Source Sink Source Sink

Rules Governing Data Flow Diagramming Process Source/Sink Rule 10: A source/sink has a noun phrase Supplier

Rules Governing Data Flow Diagramming Process A data flow has only one direction of flow between symbols It may have both direction flows between a process and a data store to show a read before an update Later it is indicated by two separate arrows Generate Orders Generate Orders

Rules Governing Data Flow Diagramming Process A fork in a data flow means that exactly the same data goes from a common location to two or more different processes, data stores, or sources/sinks. There should not be a variation in duplication A A B A

Rules Governing Data Flow Diagramming Process A joint in a data flow means that exactly the same data comes from any of two or more different processes, data stores, or sources/sink to a common location Only similar data flows can be joined A A B A

Rules Governing Data Flow Diagramming Process A data flow cannot go directly to the same process it leaves. There must be at least one other process which handles the data flow, produces some other data flow, and returns the original data flow to the beginning process B A A A C

Rules Governing Data Flow Diagramming Process A data flow to a data store means update (delete or change) Generate Orders Delete or changed data

Rules Governing Data Flow Diagramming Process A data flow from a data store means retrieve or use Generate Orders Retrieve/Use

Rules Governing Data Flow Diagramming Process A data flow must have a noun phase label Updated stock

DFDs Exercises

Data Flow Diagrams Examples of correct uses of data store symbols in a data flow diagram. [1]

Data Flow Diagrams

Data Flow Diagrams Entity can be connected with a process only Examples of correct uses of external entities in a data flow diagram.[1]

Data Flow Diagrams

Data Flow Diagrams

DFD Errors

DFD Errors