DFD(Data flow Diagram)• Data flow diagram is a graphical representation of data flow through a information system.• DFDs used for visualization of data processing, shows what kinds of information will be input and output from the system.• DFD shows where the data will come from and go to, and where the data will be stored.• Example -
DFD• Process Transform of incoming data flow(s) to outgoing flow(s).• Data Flow Movement of data in the system.• Data Store Data repositories for data that are not moving. It may be as simple as a buffer or a queue or a s sophisticated as a relational database.• External Entity Sources of destinations outside the specified system boundary.
Levels of DFD• The DFD may be used for any level of data abstraction. DFD can be partitioned into levels. Each level has more information flow and data functional details than the previous level.• Like level 0 DFD level 1 DFD.
Decision Table • A decision table lists Combinations causes and effects in aCauses Values 12345678 matrix. Each column represents a uniqueCause 1 Y, N YYYYNNNN combination.Cause 2 Y, N YYNNYYNN • Purpose is to structureCause 3 Y, N YNYNYNYN logic. • Cause = condition,Effects Effect = action = expectedEffect 1 X X X resultsEffect 2 X X X
Structure of Decision Table The four quadrantsConditions Condition alternativesActions Action entries
Decision Chart• A decision chart is a decision support tool that uses a graph or model of decisions and their possible consequences, including chance event outcomes, resource costs, and utility.• Every decision chart begins with what is termed a root node, considered to be the "parent" of every other node. Each node in the tree evaluates an attribute in the data and determines which path it should follow.• Decision chart helps for analysis the data.
Structure Chart• Describe functions and sub-functions of each part of system (in more detail than a DFD)• Show relationships between common and unique modules of a computer program• Hierarchical, Modular structure – Each layer in a program performs specific activities – Each module performs a specific function
Steps in drawing a structure chart• Review the DFDs and object models• Identify modules and relationships• Add couples, loops, and conditions• Analyze the structure chart, the DFDs, and the data dictionary
Structure ChartStructure Chart symbols • Rectangle represents a represent module (program or• Modules subroutine) (sequential logic) • Control Modules• Conditions (decision logic) (mainline) branch to sub-• Loops modules (iterative logic) • Library modules are• Data couples reusable and can be invoked from more than• Control couples one Control Module elsewhere in the system.
Structure Chart for EntireCalculate Payroll Program
Summary - Structure Charts– Show the relationships among program modules– Structure Chart consists of: • Modules - Related program code organized into small units that are easy to understand and maintain • Data couples - Data passed between modules • Control couples - Data passed between modules that indicates a condition or action to another module (e.g. End of File) • Conditions - determines what subordinate module a control module will run • Loops - Indicates one or more subordinate modules are repeated– Structure Charts are based on the DFD and Data Dictionary