Structured Analysis and Structured Design (SA/SD)
Structured Analysis and Structured Design (SA/SD) is a diagrammatic notation that is designed to help people understand the system. The basic goal of SA/SD is to improve quality and reduce the risk of system failure. It establishes concrete management specifications and documentation. It focuses on the solidity, pliability, and maintainability of the system.
Basically, the approach of SA/SD is based on the Data Flow Diagram. It is easy to understand SA/SD but it focuses on well-defined system boundary whereas the JSD approach is too complex and does not have any graphical representation.
SA/SD is combined known as SAD and it mainly focuses on the following 3 points:
SA/SD involves 2 phases:
- Analysis Phase: It uses Data Flow Diagram, Data Dictionary, State Transition diagram and ER diagram.
- Design Phase: It uses Structure Chart and Pseudo Code.
1. Analysis Phase:
Analysis Phase involves data flow diagram, data dictionary, state transition diagram, and entity-relationship diagram.
- Data Flow Diagram:
In the data flow diagram, the model describes how the data flows through the system. We can incorporate the Boolean operators and & or link data flow when more than one data flow may be input or output from a process.
For example, if we have to choose between two paths of a process we can add an operator or and if two data flows are necessary for a process we can add an operator. The input of the process “check-order” needs the credit information and order information whereas the output of the process would be a cash-order or a good-credit-order.
- Data Dictionary:
The content that is not described in the DFD is described in the data dictionary. It defines the data store and relevant meaning. A physical data dictionary for data elements that flow between processes, between entities, and between processes and entities may be included. This would also include descriptions of data elements that flow external to the data stores.
A logical data dictionary may also be included for each such data element. All system names, whether they are names of entities, types, relations, attributes, or services, should be entered in the dictionary.
- State Transition Diagram:
State transition diagram is similar to the dynamic model. It specifies how much time the function will take to execute and data access triggered by events. It also describes all of the states that an object can have, the events under which an object changes state, the conditions that must be fulfilled before the transition will occur and the activities were undertaken during the life of an object.
- ER Diagram:
ER diagram specifies the relationship between data store. It is basically used in database design. It basically describes the relationship between different entities.
2. Design Phase:
Design Phase involves structure chart and pseudocode.
- Structure Chart:
It is created by the data flow diagram. Structure Chart specifies how DFS’s processes are grouped into tasks and allocate to the CPU. The structured chart does not show the working and internal structure of the processes or modules and does not show the relationship between data or data-flows. Similar to other SASD tools, it is time and cost-independent and there is no error-checking technique associated with this tool.
The modules of a structured chart are arranged arbitrarily and any process from a DFD can be chosen as the central transform depending on the analysts’ own perception. The structured chart is difficult to amend, verify, maintain, and check for completeness and consistency.
- Pseudo Code:
It is the actual implementation of the system. It is an informal way of programming that doesn’t require any specific programming language or technology.