Visio is in essence a diagramming tool based on shapes and connections. The product has evolved to include areas such as design, documentation and software modelling.

Even though it was only recently acquired by Microsoft, Visio has for a long time been deeply integrated into Windows. Visual Basic for Applications is built in, and Visio exposes a complete object model so that other applications can control its features programmatically.

Developers can use Visio as a front-end for custom applications. For example, an office designer might use it to plan where staff will sit, calculate the cost and initiate an order for furniture. Microsoft is using a Visio application as a core part of its forthcoming BizTalk server, for managing business processes, exploiting its ability to provide drag-and-drop design together with code generation and programmatic control of other application components.

A Visio shape is a sophisticated drawing object, with a huge range of formatting options and the ability to be merged and grouped. Shapes also support data and events. In Visio's office layout shapes, for instance, each item has custom properties to supply an inventory number and an owner. Events fire when shapes are added to a diagram, clicked or modified. Shapes can also be categorised into layers, so you can show or hide selected objects.

Visio connectors are equally sophisticated. You can specify connection points and routing behaviour, so that connectors reposition themselves intelligently as a diagram grows.

For general-purpose diagramming, such as creating flow charts, organisation charts, or building your own charts from scratch, the Standard edition is a good choice. The product has been extended, with numerous specialist macros and stencils, Visio's term for custom shapes. The Technical edition has stencils for electrical, civil and mechanical engineering, and architecture.

The Professional edition targets the IT industry, with basic network design and diagramming, and documentation for database, software and internet development. The Enterprise edition is also IT-oriented, but with more complete stencils and tools. It is the most expensive, but does not include all the features in Technical, so if you model databases and design electrical circuits, you'll need both.

Visio Enterprise can automatically discover a network and diagram it, and there is full support for unified modelling language (UML). It is a complete modelling environment, with its own navigator and the ability to check a model's integrity.

You can generate code for C++, Java or Visual Basic and reverse engineer existing code in Visual Studio projects. In the same way, the database modeller lets you generate DDL (Database Definition Language) scripts, so you can first model and then create a database. You can also reverse engineer existing databases. With such strong development tools, it would make sense for Microsoft to incorporate some form of Visio into Visual Studio, rather than the current Visual Modeller, which is based on a Rational product.

A couple of years ago Visio absorbed a product called InfoModeler, with its intuitive object-modelling technique ORM (Object Role Modelling), which uses natural language facts to capture business rules. ORM lives on in Visio 2000, with its own shapes and tools.

Seasoned Visio users will not find this a radical upgrade. The most noticeable change is in the interface, which has new docked windows, a diagram explorer, and page tabs for navigating complex documents. You can now save diagrams as HTML and embed hyperlinks into shapes. There is also improved network discovery with auto-layout and support for importing structures from Active Directory, NDS (Novell Directory Services) and LDAP services. Many other features have enhancements of detail, listed on Microsoft's Visio website.

Any evaluation of Visio depends largely on what you want it for. Visio scores highly on versatility, but may take second place to more specialist tools in any particular niche. For general-purpose business diagramming, it is superb. It is also great value for software developers, with tools for everything from designing an interface to advanced modelling.

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