MIS

Unit V

DATA FLOW DIAGRAM

• A data-flow diagram (DFD) is a graphical representation of the "flow" of data through an information system. DFDs can also be used for the visualization of data processing (structured design).
• DFD can be defines as a diagram about the data flow between external agents (sources/ sinks) and the processes and data stores within a system

• A Data Flow Diagram (DFD) is also known as a Process Model. Process Modeling is an analysis technique used to capture the flow of inputs through a system (or group of processes) to their resulting output. The model is fairly simple in that there are only four types of symbols – process, dataflow, external entity, data store.

Key Components:

Data Flow Diagram for a Banking System

Be aware of the basic rules for Process Modeling:

• 1. A series of data flows always starts or ends at an external agent and starts or ends at a data store. Conversely, this means that a series of data flows cannot start or end at a process.
• 2. A process must have both data inflows and outflows.
• 3. All data flows must be labeled with the precise data that is being exchanged.
• 4. Process names should start with a verb and end with a noun.
• 5. Data flows are named as descriptive nouns.
• 6. A data store must have at least one data inflow.
• 7. A data flow cannot go between an external agent and a data store, but a process must be in between.
• 8. A data flow cannot go between to external agents, but a process must be in between.
• 9. A data flow cannot go between to data stores, but a process must be in between.
• 10. External agents and data flows can be repeated on a process model in order to avoid lines crossing, but do not repeat processes.

DATA DICTIONARY

• A data dictionary is a collection of descriptions of the data objects or items in a data model for the benefit of programmers and others who need to refer to them.
• When developing programs that use the data model, a data dictionary can be consulted to understand where a data item fits in the structure, what values it may contain, and basically what the data item means in real-world terms.
• For example, a bank or group of banks could model the data objects involved in consumer banking. They could then provide a data dictionary for a bank's programmers. The data dictionary would describe each of the data items in its data model for consumer banking (for example, "Account holder" and ""Available credit").

DATABASE MANAGEMENT SYSTEM

• Collection of interrelated data
• Set of programs to access the data
• DBMS contains information about a particular enterprise
• DBMS provides an environment that it both convenient and efficient to use

Purpose of database systems

• Data redundancy and inconsistency
• Difficulty in accessing data
• Data isolation – multiple files and formats
• Integrity problems
• Atomicity of updates
• Concurrent access by multiple users
• Security problems

Database administrator

• Coordinates all the activities of the database system; the database administrator has a good understanding of the enterprise’s information resources and needs.
• Database administrator’s duties include:
• Storage structure and access method definition
• Physical organization modification
• Granting user authority to access the database
• Specifying integrity constraints
• Monitoring performance and responding to changes in requirements

Database users

• Users are differentiated by the way they expect to interact with the system
• Application programmers – interact with system through DML calls
• Sophisticated users – form requests in a database query language
• Specialized users – write specialized database applications that do not fit into the traditional data processing framework
• Naive users – invoke one of the permanent application programs that have been written previously