The Water Distribution System

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The water distribution system is an example of a system described in UML and that a system can be described by its observed properties.

The diagram below is a UML use case model of a modern urban distribution system and depicts how water is initially stored, used and then returned to the natural environment after treatment. The objective is to show that a system can be broken down into processes, and studied by delimitation.

We enjoy analysing and describing systems using UML which helps us when trying to understand complex systems and documents for translation.

I developed this diagram at a time when we were building our house and was wondering about the cost of connecting to the water distribution network, but the interest stems from an earlier college project which aimed to calculate net water usage in a valley water system.

We installed a simple drainage system into the soil for run-off water but as we live in a built-up area, were obliged to connect our house to the waste treatment system, rather than use a cesspit. So I started thinking about what happens to our water behind the scenes and developed three UML diagrams to describe the observed process.

The first diagram is a use case diagram which aims to include the principal actors and processes involved in the water treatment and usage cycle.

water distribution system use case

Identifying processes

It identifies five main activities:

  • Water storage in the sea, on land, in waterways and reservoirs
  • Distribution of water to and away from users
  • Water usage by principle users
  • Water cleaning after use
  • Infrastructure management

Thames Water is an example of an actor which manages and processes water and manages a water distribution system.

The use case diagram identifies the significant actors. Use cases and processes are interchangeable, but a use case might be viewed differently by different actors.

Management of the water distribution infrastructure

The water distribution system relies on infrastructure, which must be managed and maintained. This infrastructure includes the piping systems for clean and foul water, the cleaning stations and the extensive human resources required to maintain the system operational.

the water distribution system relies on managed infrastructure

Activity diagram

The second activity diagram identifies the main activities involved in the system.

The three main activities that water encounters, therefore, are its storage, usage and cleaning to return to the start of the cycle. Environmental consequences exist depending on the quality of the cleaning system.

The measure of the success of recycling is the quality of the water that exits the system.

Physical flows in the water distribution network

The third diagram aims to use the sequence diagram to map the physical flows of water between the different entities it encounters in the cycle.

Documenting systems

The model aims to demonstrate the importance of the water distribution network and an initial understanding of the significant infrastructure involved.

Such a description of a system might form the basis of documentation used in exchanges between industrial actors. This model is part of the overall idea that it is possible to represent the world as a system.

Systems theory states that it is sufficient to define the boundaries of the system to describe its function. The system is described by its observable properties. The value of the description depends on the context of its use.

The model may be a useful starting point for appraising the water distribution system rather than a full and perfect description. It could form the basis of further development, critical analysis and ultimately improvement.

A secondary objective is to demonstrate the value of visual methods. UML being a structured language, the symbols and links incorporate meaning. Diagram objects such as use case, activity and sequence diagram describe the system.

Consider also the importance of documentation when dealing with complex systems. I use models and modelling to describe systems when I need to understand a new domain.


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