Systems Analysis and Design Context Diagram and Data

Systems Analysis and Design Context Diagram and Data Flow Diagram

Introduction n Systems analysis phase ����� 3 stages n n n ����������� (Require ments determination) ����������� (Requir ements analysis) ����������� (Eval uation of alternatives)

Data Flow Diagrams n ������ DFDs ������ 4 ��� n n n Process Data flow Data store External entity ���������� DFDs ��������� n n Gane and Sarson Yourdon

������ DFDs Diagrams

Data Flow Diagrams n Data flow symbol n n n ��������������� 1 item ����� process ������ 1 data flow ��� (������� ( customer order

Data Flow Diagrams n Data store symbol n n n ������������ ��������� data repository ������������� process �������� 1 data flow ��� employee

������ Context Diagram

������ context diagram

Diagram 0 n n ���������� context diagram ���� process ������ , data flows, external ��� data stores

Diagram 0

Diagram 0 n n ����������� context diagram (exploded ���� partitioned or decomposed ( ����������� overview ���� level 0 diagram

Diagram 0

Data Flow Diagrams n n Diagram ������������������� (level ���� explode) ���������� n n n Leveling Balancing Data stores

Leveling or Exploding

Balancing

Data Stores

Data Dictionary n n �������� data repository ���������� n n n Data flows Data stores External entities Processes Data elements (data items, fields) Records (data structures)

Data Dictionary

Process Description Tools n ���������� process �� DFDs ������ 3 logical structures ���� n n n Sequence Selection Iteration

Process Description Tools: Sequence

Process Description Tools: Selection

Process Description Tools: Iteration

Process Description Tools n ��������� (Structured English) ����� process ������ sequence, selection, ��� iteration

Process Description Tools: Structured English

Process Description Tools n �������� (Decision tables( n n ���� logical structure ������ process logic ���������������������

Process Description Tools: Decision Table

Process Description Tools: Decision Table

Process Description Tools n ������ (Decision trees( n n Graphical representation that shows a decision table’s conditions, actions, and rules Logic structure is shown horizontally Easy to construct and understand Decision table is better in complex situations

Process Description Tools: Decision Table

Process Description Tools: Decision Trees

Logical Versus Physical Models n Sequence of models n n A physical model shows how the systems’ requirements are implemented Create a physical model of the current system Develop a logical model of the current system After the current system is understood, create a logical model of the new system

Logical Versus Physical Models n Four-model approach n Four models Physical model of the current system n Logical model of the new system n Physical model of the new system n

Logical Versus Physical Models n Four-model approach n Major benefit is having a better grasp of the current system functions before making any modifications n Major disadvantage is added time and cost needed to develop a logical and physical model of the current system