UML, Case Tools, DFD, ER-M Vocabulary

UML Vocabulary

to learn UML Vocabulary, click this UML Vocabulary List

Case Tools

to learn UML Vocabulary, click this Case Tools

DFD ( Data-Flow Diagram )

There are four basic symbols constructs of the DFD:

• A Process in Gane and Sarson is represents by the rounded rectangle.
  A Process in Yourdon and Coad is represents by the circle.
  Process consist of ID and Process name for easy referencing;
• Data Store or Data Repository.
  Data Stores in Yourdon and Coad represents by the parallel lines;
  Data Stores in Gane and Sarson represents by the open-ended rectangle.
  Data Store or Data Repository consist of Data Store Label and Data Store Name.
• Data Flow Connector represents by the arrow line;
  Data Flow Connector may consist of Data Flow Connector Note or Data Flow Connector Label.
• External Entity or Actors or Sources or Sinks, and Terminators is represents by the rectangle.

There are various DFD in-depth analysis with multiple detail levels:

1. A context diagram or level 0 DFD, which shows a system as a single Process, External Entity, Data Flow Connector and does not contain any data storage.
2. A level 1 diagram provides greater detail, focusing on a system’s main functions.
• A level 1 should not have more than nine process symbols.
• Use a unique reference number for each process symbol. (1, 2, 3,...); 
• Another way to avoid crossing lines is to duplicate an external entity or data store. Use a special notation such as an asterisk, to denote the duplicate symbol.
3. Diagrams that are level 2 or higher illustrate a system’s functioning with increasing detail.
• It’s rare for a DFD to go beyond level 2 because of the increasing complexity, which makes it less effective as a communication tool.
• Other process numbers are in the hierarchy of: (1.1, 1.2, 1.3, ..., 2.1, 2.2, 2.3,...); (1.1.1, 1.1.2, 1.1.3,...).

Data flow diagrams are categorized as:

• A logical data flow diagram focuses on the business and how the business operates. We can ignore implementation specifics such as, computer configuration, data storage technology, communication or message passing methods by focusing on the functions performed by the system, such as, data collection, data to information transformation and information reporting.
• A physical data flow diagram shows how the system will be implemented, including the hardware, software, files, and people in the system. It is developed such that the processes described in the logical data flow diagrams are implemented correctly to achieve the goal of the business.

ER-M ( Entity Relationship-Model )

The main constructs of the ER-M:

• Entities are represented by the rectangles.
• Strong Entity represented by the rectangles;
• Weak Entity represented by the double rectangles.
• Relationships are represented by the diamond shapes.
• Attributes are represented by the oval shapes:
• Key Attribute is represented by the oval shape with underline text;
• Composite Attribute is represented by the oval shape with bold text;
• Multivalued Attribute is represented by the double oval shape;
• Derived Attribute is represented by the dashed oval shape;
• Associated attributes / Cardinality : specifies the numerical attribute of the relationship between entities. It can be :
• one-to-one; 1 - 1
• many-to-one; * - 1 or M - 1
• many-to-many; * - 1 or M - M
• Connecting lines, solid lines.

ERD Models

The level of abstraction visualized / The level of detail you want to show:

1. conceptual ERD;
2. logical ERD;
3. physical ERD;

Conceptual ERD or data model contain :

• entities;
• relationships;

Logical ERD or data model contain:

• defining additional entities that are operational and transactional;
• relationships;
• attributes 

Physical ERD or data model contain: 

• defining entities;
• relationships;
• showing primary and foreign keys of entities instead of just their abstract semantic names. For this type of ERD, 
• attributes, cardinality and attributes types will often be listed to represent the columns of the real database table.