Interaction Modeling- Sequence and Collaboration

Most of the items in sequence and collaboration categories overlap. The sequence model emphasizes events in the time element of the interaction while the Collaboration models try to show relationships between objects and components.

Sequence Diagram

Sequence Diagrams have Objects as columns, and timelines as vertical ‘rows’.

 The time axis is down the page. The vertical rectangles indicate activation of a class, while the dotted vertical lines represent the life of the object. One can adjust the length of each ‘time’ feature.

Messages between objects are represented by horizontal arrows. They can be either synchronous (acknowledging) or asynchronous (not acknowledging). The dotted arrow is a response. The sequencing of the messages are represented by their order from the top of the chart.

In the above example, the heater sends signals to the thermostat. When a certain point is reached, the thermostat sends a message to the switching system, which, in turn responds by shutting down the heating system.

Collaboration Diagrams

Collaboration diagrams concentrate on the messaging interaction between objects from a functional point of view, rather from a sequential point of view.


In the diagram above, 5 objects are linked in the order entry process. The salesman enters the system with his ID and gets a new sales order. The sales order object then checks the customer file for the customer’s ID and the file checks the Accounting object to assure that the customer’s credit is good.

Then, the sales order object allows the entry of line items for this order, checking the inventory for each item to see whether it is in stock. The process certainly could be extended to provide for back order, of manufacturing activity, as well as shipping, billing and collection, with inventory and associated accounting entries being made on the way.

During this collaboration process, constraints and methods can be attached to the messages to notify other objects, make data entries into a database, send email and generate exception reports. Presently, the level of sophistication is somewhat below what one could expect from a developer program which specializes in process engineering, such as VisGen, or Case Tools. However, one should also keep in mind that once Excel and Word were also rated as ‘second tier’ products. The Vision version of UML that accompanies Microsoft’s .NET package is certainly rich enough with features to design all but the most involved multi-year project at the current time. In addition, Microsoft Project is an OLE compliant product whose features can easily be integrated into the process of developing software.


This link provides review on book dealing with UML.

This link provides list of comprehensive books on UML.

This book deals with UML and is intended to be read by people involved in the production of object-oriented software systems.


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This page revised   April 30, 2007