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Web Services Soup to Nuts

Simplified Web services development using visual tools

When you set out to develop a new Web service, do you start banging out angle brackets right off the bat, or do you sketch out the logic of your service first? For most engineers, the graphical approach to implementing business logic is much more accessible. Only after a picture is created does the complexity of translating it into code come into play.

Though Web services are intended to simplify communications, developing them manually can be anything but simple. Altova has added visual Web services development and implementation capabilities to two of its most popular products, giving developers the ability to build a Web service from start to finish without becoming mired in manual code writing.

Altova provides support for developing all XML-related technologies, including Web services, in its XML Suite. By using these tools, developers can design and implement a Web service using a purely graphical approach. This article discusses this visual Web services design and implementation process and how it removes much of the complexity associated with Web services development.

Graphical WSDL Creation and Editing
Best practices dictate that designing the WSDL should be the first step in architecting Web services. By building the WSDL that will act as the Web services interface first, client and server programmers can implement their respective programming contract for accessing the service using any language or operating system, since WSDL is standards-based and programming language-neutral. That means a Web services client application can talk to a server application running on a different platform without interoperability issues. This built-in interoperability also means that the service can be reused easily. Unfortunately, given the complexity of WSDL and WSDL development, this design step is often overlooked or undertaken only as an afterthought.

Altova XMLSpy 2006 is an XML development environment that includes a graphical WSDL editor that removes much of the complexity associated with WSDL development by enabling a completely visual process. Instead of working solely with a text view, developers can build their WSDL files graphically, with full validation and editing help. This removes the complexity barrier to the design-before-implementation development approach.

The XMLSpy graphical WSDL editor in Figure 1 supports creating, editing, visualizing, and validating any WSDL file. It displays the WSDL file structure as well as the WSDL elements grouped by operations, portTypes, bindings, and services. You can manipulate the file by dragging and dropping elements, and context-sensitive windows and entry helpers provide useful editing options.

When you create a new WSDL file from scratch, XMLSpy presents you with a graphical representation that consists of a box for each type of WSDL element: operations, portTypes, bindings, and services. This visual representation allows you to easily see the structure of the WSDL and edit each portion in a logical way. Since the "skeleton" WSDL structure has already been created, you can edit each portion separately in any order - whatever makes the most sense to you. In general, to create a WSDL, the following must be completed:

  • Name the service
  • Associate ports with the service
  • Associate a binding name, type, and location for each port
  • Add operations in the operations component
  • Name each operation, then add input, output, and/or fault elements
  • Validate the WSDL file and correct any validation errors
There are several options and helpful features available in XMLSpy for completing these steps, as described below.

To the right of the design window, the overview window reveals the structure of the WSDL document. It displays the components of the WSDL file in a tree view in the sequence in which they appear in the code. You can expand and collapse components to reveal and hide subcomponents. Selecting a component in the overview window or from within the design itself displays that component and its properties in the details window, for example, the name, binding, and location of each port. These entries are editable by hand or by using context-sensitive drop-down menus.

The graphical WSDL display helps you immediately understand the relationships between the different components in the file and add new elements in a straightforward way. The operations component of the design window lists all of the operations in the WSDL, and each is connected to its respective port type with a color-coded line. Expanding any operation displays its input and output components, and a context-sensitive right-click menu lets you append, insert, or delete operations (Figure 2), as well as add input and output messages to any operation. To associate a port type with an operation, simply drag the operation to the desired port - the same is true for binding and services associations.

In addition to the colored links, clicking any port type in the port type component highlights all associated operations in the operations component and in the overview window. Each port type is also linked to the associated binding with the same color-coded line, and bindings are linked to their respective services in the services component. At a glance, you can tell which operations are associated with which port types, bindings, and services, and you can adjust these associations by dragging and dropping elements.

Selecting a binding lets you view or edit all relevant parameters in the details window:

  • The name attribute
  • The type attribute, which refers to the specific port type
  • The type of binding: SOAP, http/GET, http/POST
  • The transport URI, which defines the transport URI
  • The style attribute: RPC or document
You can also add, edit, and delete these connections using drag-and-drop and context-sensitive menus (right click, tool bar, or drop down - whichever you prefer).

In addition to the visual WSDL design view, XMLSpy also includes a graphical XML Schema editor. This means you can switch to and edit any schemas referenced or imported in the WSDL very easily, using a similar visual paradigm.

While you're working in the graphical view, the corresponding XML markup is built behind the scenes and is available under XMLSpy's text view tab, and you can, of course, edit the text directly in that view (Figure 3).

One last note about XMLSpy is that it also includes a WSDL documentation generator that will output documentation for any standards-conformant WSDL file. Documentation can be in HTML or Microsoft Word and is useful for giving business partners, other developers, or customers a detailed overview of the Web service interface. This feature is also useful for understanding WSDL files that are generated by other platforms.

Overall, designing WSDL using a graphical paradigm makes WSDL development more accessible and productive, which in turn makes the Web services implementation phase more straightforward.

Visual Web Services Implementation
Once a WSDL is defined, implementing the Web service that it describes involves writing the code to access the data required for each transaction. Given that even simple Web services can require thousands of lines of code, this process quickly snowballs. Altova MapForce 2006 adopts the same visual design strategy used in the XMLSpy WSDL design view for building Web services.

More Stories By Erin Cavanaugh

Erin Cavanaugh is product marketing manager for Altova (www.altova.com), creator of XMLSpy and other leading XML, data management, UML, and Web services tools. In this role, Erin manages Altova's XML-related line of tools. She has held product marketing, training, and technical copywriting roles at a variety of hardware and software firms.

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