Interoperability

Interoperability is of essential importance for a communication interface and needs to be considered on all levels.

Specification Design
The Xi interface is specified as simple as possible for then intended functionality corresponding to OPC DA, HDA, AE.
The simplicity and clean interface structure reduces the risk for interoperability issues.

Communication Base
The Xi communication is fully based on .NET and the Microsoft Communication Foundation (WCF) and WCF bases on web services standards.
In OPC applications interoperability issues were to a large part due to DCOM configuration issues. WCF is the state of the art Microsoft communication platform and is much less problematic. The rather complex configuration possibilities of WCF is addressed by Xi with:

• server side only configuration
•  a set of recommended Xi communication settings
• vendor provide utilities that create the WCF configuration based on simple application requirements choices.

Generic Xi Layers
A reference implementation of an Xi server and Xi client is available with the Xi specification. This code is split into a generic base part and an application specific implementation part.
Interoperability issues can be further reduced by using vendor toolkits and components. These products are tested and supported and are updated by the vendor.

Application Testing
Interoperability is improved most when the application developer has access to test tools and products of multiple vendors. With these available, interoperability testing becomes part of the development process.

Xi Client Testing
Xi client developers have access to Xi servers in two ways:

• Internet accessible servers
  Xi client can access Xi servers on the Internet and test with these servers without having to download and install the server. Xi server vendors are encouraged to make their servers accessible by hosting the server either on the vendor web site or on this web site. The URLs of accessible servers are listed on this site.
  
• Evaluation packages
  Most vendors provide free evaluation packages. These can be downloaded and used as interoperability test environments.

Xi Server Testing
The Xi Server developer needs client applications to test the server. Different kind of cleints are available:

• The client application in the Xi sample code has a user interface structured according the Xi interface specification.
  Individual server methods can be called. The client is well suited for initial testing.
  
• Clients from Xi component vendors
  These client applications are typically based on the vendor's components and have a more application oriented user interface. Analyzer clients automatically execute sequences of server calls.
  Downloadable client applications are listed on this site. Some of these clients are Click-Once applications that are quick to download and install.
  
• Application packages
  Vendors of application packages with Xi support usually provide free evaluation downloads. These can be used as interoperability test environments.