System design tool THEORY

35 functionality to the system-namely, the addition of new features to the existing system without disrupting operations.

2.8 System design tool

2.8.1 Data flow diagram DFD Data flow diagram is a diagram that illustrates the flow of data. Data flow diagrams can be used to present an automated system or manually with an image in the form of network graphs, symbols used in data flow diagram: 1. External entity terminal Different entities outside the system which is provide data to the system source or receive information from the system sink. External entities are not included in the system. Symbol used: Figure 2.5 External entity symbols 2. Process bubble Describe what is done by the system, serves to inform one or more output data according to the desired specifications. Each process has one or more input data and produces one or more output data. Symbol used: 36 Figure 2.6 Process symbols 3. Data flow Using data flow from an entity to another entity. Direction arrows depict the flow of data that can occur between two successive processes, from data store to process and vice versa, from the source to the process, from process to sink. Symbol used: Figure 2.7 Data flow symbols 4. Data store Data store is serves as a place to store data. A process can be take the data or to provide feedback data to the data. Symbol used: Figure 2.8 Data store 2.8.2 State transition diagram STD State transition diagram is a modeling tool that describes the nature of the time dependence on the system. STD is used to identify the system should behave as such the risk from external events. To achieving this, STD displays various types of models of behavior and outcomes and behavior which made the transition from one state to another state. 37 Presentation of STD is the basic foundation for determining behavior. STD typically used notation such as: 1. active  State, rectangle symbol State is a collection of state or an attributes that gives the details of a person or object at a time and under certain conditions. Examples such as the user fills the password, determines the next instruction. State symbol:  Transition state, directional arrow symbol  Condition Incident in the external environment can be detected by the system. This will be result in a change to the state of circumstances state waiting for X to state wait to Y. examples such as: interrupt signal and data. 2. Passive This system does not perform the control of the environment, but rather is receiving data or give any reaction systems that receive or collect data via signals transmitted by the satellite. There are two approaches in making the state transition diagram: 38  Identification of every possible state of the system and describe each one in a box, and make the relationship between the state.  Start with the first state and continued with the next state accordance with the desired flow. Here is a simple overview of STD: Condition Action Figure 2.9 State Transition Diagrams 2.8.3 Entity relationship diagram ERD According to Jeffery L. Whitten, Lonnie D. Bentley, Kevin C. Ditman, methods of analysis and design 6th edition 2004, ERD is a data model that uses some notation to describe the data in terms of entities and relationships described by the data. There are 3 kinds of relationship cardinality, there are: 1. One-to-one, which means that each tuple in the entity A associated with at most one tuple in the entity B. 2. One to many, that means a tuple in the entity A may be associated by many tuple in the entity B, but not vice versa, where each tuple in the entity B associated with at most one tuple in the entity A. State X State Y 39 3. Many-to-one, which means that each tuple in the entity A may be associated with at most one tuple in the entity, but not vice versa, where each tuple in the entity A associated with at most one tuple in the entity B. 4. Many-to-many, which means that each tuple in the entity A may be associated by many tuple in the entity B and vice versa, where each tuple in the entity B can be associated with many tuple in the entity A.

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