April 15, 2024

Conceptual Model & Annotation Diagrams for SRS Document

As we all know what software requirements specification, SRS totally describes what the software will do & how it will function. The best SRS defines how an application will connect with system hardware, human user & other programs. There are certain diagrams included in an SRS to get the real-time solution for software development. These diagrams mainly rely on factors like operational speed, response time, availability, portability, security, and speed of recovery from adverse events.

Here we’re going to deeply discuss the various diagrams used in an SRS document along with the suitable examples.

1. Use case diagram


A use case diagram is a graphical drawing of a user’s viable interactions with a system. A use case diagram indicates various use cases and different types of users the system has. Use case diagrams will often be accompanied by other types of diagrams.

Notation & Symbol

If there's a diagram then there's a symbol/ notation for sure. They are very clear & don't involve as many types of symbols as other diagrams.

  • Use cases:

Horizontally egg-shaped symbols that represent the different uses that a user might have.

  • Actors:

Stick figures that show the user actually employing the use cases.

  • Associations:

A line symbol showing the relationship between actors and use cases. It is necessary to know which actors are associated with which use cases.

  • Packages:

A UML shape that enables putting different elements into groups.


Use Case Diagram Example

2. Data flow diagram


The data flow diagram shows how information flows through a process or system. Data flow includes data inputs/ outputs, data storage, and the various sub-processes the data moves through.

Notation & Symbol

The two main types of notation are used for data flow diagrams. One is Yourdon-Coad and another one is Gane-Sarson’s notation. The two different notation styles for different uses. Processes, data stores, external entities, and data flows are the four main entities of the data flow diagram.

  • External Entity:

Also known as actors. sources or sinks, and terminators, external entities produce and consume data that flows between the entity and the system being designed in a diagram.

  • Process:

A name ‘process’ given directly related to its function. For example ‘ship order’ can be used for process & if we’re using Gane-Sarson notation- a rectangular box symbol is used to showcase the process.

  • Data Storage:

Data storage is represented with an arrow symbol. A symbol that indicates the flow direction. This data could be electronic, written, or verbal- any of them.


Data Flow Diagram Example

3. Sequence Diagram


Sequence Diagrams are interaction diagrams that detail how operations are working. They find the interaction between objects in the context of a collaboration. Sequence Diagrams are based on time and they show the correct order of the interaction.  There is a vertical axis of the diagram to represent time, what messages are sent, and when.

Notation & Symbol

  • Actor:

A symbol that is played by an entity that interacts with the subject. External to the subject in the sense that an instance of an actor is not a part of the instance of its related subject.

  • Lifeline:

A lifeline symbol shows an individual participant in the Interaction.

  • Activations:

Activation- A thin rectangle on a lifeline symbol used in a sequence diagram. It represents the period during which an element is performing an operation.

Various Messages

  • Call Message:

A message defines a particular communication bond between the Lifelines of an Interaction.

  • Return Message:

A message defines a particular responsive communication between the Lifelines of an Interaction.

  • Self Message:

A self message represents the invocation of a message of the same lifeline.

  • Recursive messages:

A recursive message is a kind of message that represents the invocation of a message of the same lifeline.


Sequence Diagram Example

4. Class Diagram


Class diagrams are one of the most useful types of diagrams as they figure out the structure of a specific system by creating its classes, attributes, operations, designs, and relationships between objects.

Notations & Symbols

Member access modifiers

All classes have different access levels depending on the access modifier (visibility). Here are the access levels with their corresponding symbols:

  • Public (+)
  • Private (-)
  • Protected (#)
  • Package (~)
  • Derived (/)
  • Static (underlined)


Particular for a system, a template for creating objects and implementing behavior.

  • Name-  The first row in a class shape.
  • Attributes- The second row in a class shape. A separate line is used to show every attribute of the class.
  • Methods- The third row in a class shape. Recognized as operations, methods are displayed in list format.
  • Data types:

Classifiers that define data values. The values that can model both primitive types and enumerations.

  • Interfaces:

A group of operation signs and attribute definitions that define cohesive behaviors.

  • Enumerations:

Representations of user-side data types. An enumeration includes groups of identifiers that indicate values.

  • Artifacts:

Model elements that represent stable entities like documents, databases in software systems.


Class Diagram Example

5. Activity Diagram


There are Activity diagrams, along with use case and state machine diagrams, which are counted as behavior diagrams. The main reason behind this- they describe what must actually happen in the modeled system.

Notations & Symbols

  • Action:

In SRS, actions are symbolized with round-edged rectangles.

  • Decision node:

A conditional branch in the flow. It includes a single input and two or more outputs. The diamond shape is being used to show this node.

  • Control flows:

Controller that shows the flow between continuous steps in the diagram.

  • Start node:

Symbolizes the beginning of the activity. Generally, represented by a black-circle symbol.

  • End node:

The end node is the final step in the activity. The outlined black circle is the notation of an end node.


Activity Diagram Example

In Ending

These are the main & most important diagrams available in the SRS documentation. They’re a perfect example of storing more data in just a diagram & carrying out more space for other activities. All diagrams are part of the process and trying to process & flow easier.

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