We all know the idea of sustainability from our daily life. But is it possible to apply this idea to software development? I think yes.
Sustainable Service Design is a practical approach to design and implement software services with a great level of reuse both at technical and business levels. It is based on the following four principles:
The advocates of Service Orientation always pointed out that SOA comprises 50% technology and 50% business. At BiPRO this vision becomes true. BiPRO is a standardization organization for the insurance industry. BiPRO has members from the entire market including well known insurance companies and agents. By standardizing services at the business level using proven technical standards, BiPRO really takes the SOA idea to the next level. BiPRO conformant services are reusable and highly interoperable. Development is contract first, based on open standards such as WSDL and XSD. It is really impressive to see what BiPRO already achieved.
On 25.6.-26.6. June BiPRO-Day 2014 is going to take place in Düsseldorf Germany.
At the event I am going to give a live coding session. In particular I am going to show how to implement and secure BiPRO services using current Web Service standards such as JAX-WS, SAML, WS-Security and WS-SecureConversation. Attendees can see how the implementation works with JBoss Wildfly, Apache CXF and .NET. Moreover they can take a peek into the future of BiPRO standards in the area of security.
I hope to see you there!
Since BPMN2.0 it is not only possible to design processes but to also execute them using a process engine. The process flow has a appropriate visual representation in the standard. But executable processes are mostly data driven. They interact with external services and exchange data with them. In addition to that processes maintain their own internal state. So a common requirement is to model the process internal state and connect to external services using the service data representation. BPMN is capable to include data definitions based on WSDL and XML Schemas, although the capabilities of the tools (that I know) to visualize data are somewhat limited.
In this blogpost I would like to show you how data looks like in BPMN and how a process can be linked in a standardized way to existing services based on WSDL and XSD.
The process is as simple as possible. The service is based on a BiPRO service description. The BiPRO is a standardization organisation in the German insurance market that standardizes processes and services at a technical and business level.
Below you see a simplyfied version in plain BPMN (when you import the bpmn below you will only see the events and tasks).
<?xml version="1.0" encoding="UTF-8"?>
<definitions id="definitions" xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL"
<!-- WSDL Import -->
<!-- Item definition. Link to the external WSDL/XSD structure. structureRef: QName of input element -->
<itemDefinition id="getQuoteRequestItem" structureRef="nachrichten:getQuote" />
<itemDefinition id="getQuoteResponseItem" structureRef="nachrichten:getQuoteResponse" />
<!-- Message definitions. Link to the item definition. Can be visualized by using DI -->
<message id="getQuoteRequestMessage" itemRef="tns:getQuoteRequestItem" />
<message id="getQuoteResponseMessage" itemRef="tns:getQuoteResponseItem" />
<!-- Interface definition. implementationRef = QName of WSDL Port Type -->
<interface name="Komposit Interface" implementationRef="bipro:KompositServicePortType">
<!-- Operation: implementationRef = QName of WSDL Operation -->
<operation id="getQuoteOperation" name="getQuote Operation" implementationRef="bipro:getQuote">
<!-- Links to the message definitions -->
<!-- Datasources and targets for the service call (process state). Can be visualized by using DI and dataObjectReferences -->
<dataObject id="dataInputOfProcess" name="Input for webservice" itemSubjectRef="xs:string"/>
<dataObject id="dataOutputOfProcess" name="Output for webservice" itemSubjectRef="xs:string"/>
<!-- Process start -->
<startEvent id="start" />
<sequenceFlow id="flow1" sourceRef="start" targetRef="initScript" />
<!-- Initialization of process data -->
<scriptTask id="initScript" scriptFormat="groovy" name="Initialize process">
def temp = "184.108.40.206.1"
<sequenceFlow id="flow2" sourceRef="initScript" targetRef="webService" />
<!-- Web Service call -->
<serviceTask id="webService" name="Call getQuote" implementation="##WebService" operationRef="tns:getQuoteOperation">
<!-- Defines the inputs and outputs and links to item definitions -->
<dataInput itemSubjectRef="tns:getQuoteRequestItem" id="dataInputOfServiceTask" />
<dataOutput itemSubjectRef="tns:getQuoteResponseItem" id="dataOutputOfServiceTask" />
<!-- Defines the mapping between process data and service input -->
<!-- Defines the mapping between process data and service output -->
<sequenceFlow id="flow3" sourceRef="webService" targetRef="end" />
<!-- Process end -->
<endEvent id="end" />
Now let’s look at the example step-by-step.
1. Import the service: Line 16-18 imports the WSDL file that includes the types and messages used by the external service that we want to call from the process.
2. Define the items: Line 21-22 defines items that act as links to the types defined in the imported WSDL and XSD files.
3. Define the messages: Line 25-26 defines messages to be used in the interface definition that we see in the next step. Messages can be visualized by modeling tools provided that DI Information is present in the model.
4. Define the interface: The interface is the equivalent to the WSDL port type in BPMN. It is defined in line 29-36. So far we have itemDefinitions that link to the XSD-messages and an interface that links to the WSDL-port type. The inMessageRef and outMessageRef elements use the messages defined in step 3 to indirectly reference the itemDefinitions.
5. Define the process variables: The process maintains state. This state is defined in the form of dataObjects in line 41-42. Please note that the links to the external service are defined outside the process (which begins in line 38). The dataObjects are defined inside the process as they represent the data that is maintained by the respective process instances. By the way, when importing the process in a modeling tool, dataObjects are not visualized. To visualize dataObjects as a paper sheet, dataObjectReferences can be used. In this simple example we just use a string as input and output which transports a version information send to the BiPRO service and back. In a more complex senario this could be a type from an imported XSD.
6. Initialize the process: A simple BPMN script task (line 50-55) is used to initialize the dataObject dataInputOfProcess. It just sets the version to 220.127.116.11.1.
7. Link the serviceTask: The most complex part is the serviceTask (line 60-102). The operationRef attribute (line 60) links to the operation which is part of the interface definition (line 31). This is the web service operation to be called when the serviceTask is executed. The serviceTask comprises the elements ioSpecification (line 63-72), dataInputAssociation(line 75-86) and dataOutputAssociation (line 89-100). ioSpecification can be seen as a logical port that describes the service input and output from the perspective of the service. The itemSubjectRef attribute on the dataInput and dataOutput elements (line 64-65) link to the itemDefinitions (line 21-22) and as such to the data structures in the WSDL files. The id together with the inputSet and outputSet (line 66-71) define the connection points the serviceTask offers for sending and receiving data. dataInputAssociation and dataOutputAssociation map the dataObjects (process data) to the connection points or in other words to the request and response structures of the service (service data).
When the serviceTaskwebService is called, the process data from the dataObjectdataInputOfProcess is copied to the web service request message nachrichten:getQuote/BIPROVersion. Then the service is called. After the service call finished, the version is copied from the response message nachrichten:getQuoteResponse/BIPROVersion to the dataObjectdataOutputOfProcess.
This blogpost has shown how to link WSDL/XSD based services to BPMN processes in a standardized way.
Even if automated process execution is not in focus, it can be important to unambiguously link services to processes to create an integrated view of the entire process including its data.
One of the most important artifacts in Service-oriented Architecture (SOA) is the service contract. The contract defines how service producers and consumers interact with each other. Most people agree that a contract first approach is the preferred way of creating service contracts. WSDL based service contracts are very common. In many projects they are generated by the respective frameworks, such as Apache CXF or Microsoft WCF. This is dangerous, as the developer looses control over the contract. This can result in missing interoperability and limited reusabilty expecially in cross platform scenarios.
From what I see, most developers know how to work with their favourite IDE, but only a few know how to create a proper service contract from scratch. I think that is caused by the tool vendors, which in most cases have better support for code based approaches.
In this post I would like to show how to create a portable contract from scratch and share some best practices.
The domain model
The first thing to think about is the domain or entity model that the service should expose. The model should be modeled in XML Schema. XML Schema is standard, portable and supported on all platforms. In fact it is a good idea to use XML Schema as the single source of model information.
The following listing defines the entity Product:
<![CDATA[Name of the productQuantity on stock
The entity Product has two attributes name and quantity. Please note that the xml elements (line 10 and 15) are abbreviated. This helps to reduce the message size on the wire, expecially important in WANs. The downside is obviously reduced readability. That is not really a problem as the contract should be documented anyway using the standard XML Schema annotation elements as shown in line 11 to 13.
This is the result:
Wouldn’t it be nice to have a common base class in order to create a more generic service contract?
Luckily XML Schema allows that. Let’s create another schema BaseTypes.xsd in which we define the base types.
Unique keyStatus of the entity
This base type Entity (line 24) defines common attributes for all entities. In XML Schema one can define enumerations as well (line 8 and 15). The enumeration EntityStatus defines the state of the entity. This is important in scenarios in which the entities are detached from the database. By marking the entities, it is easy to implement change tracking on the consumer side and just return the changed or deleted parts to the server. This saves network and processing time. EntityType is used later in our service interface to request different types of entities.
We can now import the base types into Types.xsd and change the Product type:
Name of the productQuantity on stock
You can see the import in line 9. In line 12 and 13 the base type is added to the Product type.
This is the result:
Now we have our model completely defined in XML Schema. By using imports and type inheritance one can create very modular entity models. Those models can be reused without any change by interface definitions such as WSDL and WADL for SOAP or REST services. Moreover the code models (Java, C#, etc.) can be fully generated from the schema. Every good framework has a generator tool on board. For instance Apache Axis/wsdl2java, Apache CXF/wsd2java, Silverlight/slsvcutil, .NET/svcutil, etc. The schema can be stored in a service repository in order to increase reusability amongst the organisation.
Every service operation receives a message and returns a message to the sender. Those messages should also be defined using XML Schema. The following snippet shows the message definitions. The fault messages are ommitted for the sake of simplification.
This represents a request to read business entitiesType of the entities to readUnique keys of the entities to readThis represents the read responseList of entities
Those are our messages:
ReadEntitiesRequest and ReadEntitiesResponse are bulk operations that allow to read multiple entities with one call. As you can see ReadEntitiesResponse does not return Products but Entities. Do you remember? This is our base class type for all entities. By using the base class, the message can return arbitrary entity types in the same message. This is an example for a strongly typed but yet extensible interface.
The schemas can be reused in WSDL files:
The type information and message definitions are completely externalized to individual schemas. As a result the WSDL is small. The imported types (line 4) are used to define the WSDL messages (line 7 and 10). A WADL file would look like this:
This is the product id
The types are imported (line 8 and 9) and used to define the return message (25).
By using the respective tool, such as wsdl2java or svcutil, we can completely generate the model and messages for the client and server on JEE, .NET and other platforms.
As you can see it is not too difficult to create schema based service contracts in a platform agnostic way. If you do, you will be rewarded with a great level of control, portability and reusability. Powerful features of XML Schema, such as inheritance, allow to create robust and extensible service contracts, which are the basis for interoperability. And if you want, you can even use an XML editor. 😉