IBM BPM, V8.0.1, All platforms > Authoring services in Integration Designer > Services and service-related functions > Building mediation flows
Mediation flows overview
Mediation flows intercept and modify messages that are passed between existing services (providers) and clients (requesters) that want to use those services. They are most commonly used for transforming data and accessing header information, such as JMS, MQ or SOAP headers.
Mediation modules can be deployed on the WebSphere Enterprise Service Bus or the IBM Process Server.
In SOA, services represent business functions that can be reused and combined in an ad hoc manner to create responsive business systems. These services have loosely coupled connections, rather than being connected directly to each other.
Introducing mediation flows between services enables you to process the messages that are being passed between these services. A message is a communication sent from one application or service to another application or service. Mediation flows provide the logic that processes the messages.
For example, mediation flows can be used to find services with specific characteristics that a requester is seeking and to resolve interface differences between requesters and providers. For complex interactions, mediation primitives can be linked sequentially. Typical mediations include:
- Transforming a message from one format to another so that the receiving service can accept the message
- Conditionally routing a message to one or more target services based on the contents of the message
- Augmenting a message by adding data from a data source
Stock Quote example: building a mediation flow
To illustrate a mediation flow, we will use an example of a simple mediation flow that provides stock prices. A client application provides a query containing a stock symbol and customer ID to the mediation flow, which processes the query. The customer's subscription level is determined, and depending on the level of subscription, the query is routed to the appropriate service provider. The quote that is returned from the service provider is converted into the customer's preferred currency before it is returned to the client application.
We are using a mediation flow because we want to use different interfaces from two external service providers, and expose a single interface to the client application. We need to build the service quickly, with the ability to change the application on demand, and without modeling a business process. We also want the ability to change the service provider without disrupting the service.
The following picture shows the complete mediation:
- Mediation modules
Mediation service applications are assembled and deployed as one or more mediation modules. Mediation modules are deployable units that contains mediation flows. They can be deployed on the IBM BPM or the IBM Process Server. - Mediation flow components
A mediation flow component provides a mediation service implemented using mediation flows. A mediation flow component in the assembly editor has the following parts - Mediation flows
A mediation flow consists of a sequence of processing steps that are run when an input message is received. - Mediation primitives
Mediation flows consist of a sequence of mediation primitives, which define processing steps. - Service message objects
A message is a communication sent from one application or service to another application or service. Messages in mediation flows are represented as service message objects (SMOs) - XPath
The XML Path Language (XPath) is a language used to uniquely identify or address parts of an XML document. An XPath expression can be used to search through an XML document, and extract information from the nodes (any part of the document, such as an element or attribute) in it. XPath can be used alone or in conjunction with XSLT. - Message Transformation
When you are integrating services, you usually need to transform the data into a format that the receiving service can process. Typically, interfaces and operations of disparate services are not identical, and the message from the source needs to be transformed into a format that can be accepted by the target.