Sequence Build Diagrams

Sequence Diagrams

The sequence diagram is one of the variety of interaction diagrams and is intended for modeling the interaction of the System objects in time, as well as the exchange of messages between them.

One of the basic principles of OOP is a method of information exchange between the elements of the System, expressed in sending and receiving messages from each other. Thus, the basic concepts of a sequence diagram are related to the concept Object and Message.

In the sequence diagram, objects basically represent instances of a class or entity with behavior. Objects can be users initiating interaction, classes with behavior in the System or software components, and sometimes Systems as a whole.

Objects are located from left to right in such a way that the object that initiates the interaction is at the left of the left. An integral part of the object in the sequence diagram is the life line of the object. The life line indicates the time during which the object exists in the System. The periods of activity of the object at the moment of interaction are shown using the control focus. The timeline in the chart is directed from top to bottom.

Sequence Diagrams Concept

Sequence diagrams allow the use of standard class stereotypes:

• Actor is an instance of a process participant (role in the use case diagram)
• Boundary - Class-Delimiter - used for classes that separate the internal structure of the system from the external environment (screen form, user interface, I / O device). An object with a stereotype > class, which is mostly intended to call the methods of the class with which it is associated. The boundary object shows exactly the screen form, which receives and transfers data to the handler.
• Control - Controller class - the active element, which is used to perform some operations on objects (software component, module, handler)
• Entity - Entity class - usually used to denote classes that store certain information about business objects (corresponding to a table or database element)
• Also one of the basic concepts associated with a sequence diagram is Message.

In this example you can find all most used Sequence Diagrams stereotypes for build your own diagram in BD Diagrams tool.

Facebook Web User Authentication

An example of UML sequence diagram which shows how Facebook (FB) user could be authenticated in a web application to allow access to his/her FB resources. Facebook uses OAuth 2.0 protocol framework which enables web application (called "client"), which is usually not the FB resource owner but is acting on the FB user's behalf, to request access to resources controlled by the FB user and hosted by the FB server. Instead of using the FB user credentials to access protected resources, the web application obtains an access token.