How to Draw DFD (Data Flow Diagram) and ER (Entity Relationship) Diagram
How to Draw Data Flow Diagram for final year projects ?
DFD and ER diagram is a visual representation of information flows within your application. It shows how information enters and leaves the application, what changes the information and where information is stored.
The data flow diagram begins with Level 0 and its progress to level 3, 4 and so on is possible but anything beyond level 3 is not very common.
Each level of DFD has few rules to implement.
LEVEL 0 of DFD is a simple representation of the whole application and is extremely basic
LEVEL 1 of DFD is an exploded view and is a bit more addition to level 0.
LEVEL 2 of DFD explains more detailed look of the processes that make up an information system than a level 1 DFD does and level 2 is the detailed diagram.
1. External entity:
It is an outside system that sends or receives data, communicating with the system being diagrammed. They are the sources and destinations of information entering or leaving the system. They are also known as terminators, sources and sinks or actors
3 Data store:
A data store represents the storage of persistent data required and/or produced by the process. Data stores hold information for later use, such as a database table or a membership form. Each data store receives a simple label, such as “Orders.”
4 Data flow:
A data flow represents the flow of information, with its direction represented by an arrow head that shows at the end(s) of flow connector. The Data flow route that data takes between the external entities, processes and data stores. It portrays the interface between the other components and is shown with arrows, typically labelled with a short data name, like “Billing details.”
Data flow diagrams are well suited for analysis or modeling of various types of systems in different fields like
DFD in software engineering
DFD in business analysis
DFD in business process re-engineering
DFD in agile development
DFD in system structures
How to Draw ER (Entity Relationship) Diagram for final year projects ?
- Purpose and scope: Define the purpose and scope of what you’re analyzing or modelling.
- Entities:Identify the entities that are involved. When you’re ready, start drawing them in rectangles (or your system’s choice of shape) and labeling them as nouns.
- Relationships:Determine how the entities are all related. Draw lines between them to signify the relationships and label them. Some entities may not be related, and that’s fine. In different notation systems, the relationship could be labelled in a diamond, another rectangle or directly on top of the connecting line.
- Attributes:Layer in more detail by adding key attributes of entities. Attributes are often shown as ovals.
- Cardinality:Show whether the relationship is 1-1, 1-many or many-to-many.
The main symbols used in ERD such as rectangles, diamonds, ovals and connecting lines to represent the interconnectedness of entities, relationships and their attributes. They mirror grammatical structure, with entities as nouns and relationships as verbs.
ER diagrams also are often used in conjunction with data flow diagrams (DFDs), which map out the flow of information for processes or systems.
The components and features of an ER diagram are follows
It is a definable thing such as a person, object, concept or event that can have data stored about it. Entities should be defined as nouns. Examples: a customer, student, car or product
1.1 Entity type: A group of definable things, such as students or athletes, whereas the entity would be the specific student or athlete. Other examples: customers, cars or products.
1.2 Entity set: Same as an entity type, but defined at a particular point in time, such as students enrolled in a class on the first day. Other examples: Customers who purchased last month, cars currently registered in Chennai.
1.3 Entity categories:
- Strong Entity
- Weak entity
- Associative Entity
A strong entity can be defined solely by its own attributes, while a weak entity cannot. An associative entity associates entities (or elements) within an entity set.
A candidate key to uniquely identify the entity set
Identifies the relationship between entities.
1.4 Candidate key:
A minimal super key, meaning it has the least possible number of attributes to still be a super key. An entity set may have more than one candidate key.
1.5 Super key: A set of attributes (one or more) that together define an entity in an entity set.
A relationship between two entities signifies that the two entities are associated with each other somehow. It explains how entities act upon each other or are associated with each other.
For Example, the named student might register for a course. The two entities would be the student and the course, and the relationship depicted is the act of enrolling, connecting the two entities in that way. Relationships are typically shown as diamonds or labels directly on the connecting lines.
Recursive relationship: The same entity participates more than once in the relationship.
A property or characteristic of an entity. Often shown as an oval or circle.
Multi-value: More than one attribute value is denoted, such as multiple phone numbers for a person.
It Defines the numerical attributes of the relationship between two entities or entity sets. The three main cardinal relationships are one-to-one, one-to-many, and many-many.
one-to-one example : would be one student associated with one mailing address.
A one-to-many example (or many-to-one, depending on the relationship direction): One student registers for multiple courses, but all those courses have a single line back to that one student.
Many-to-many example: Students as a group are associated with multiple faculty members, and faculty members in turn are associated with multiple students.