contract first and contract last pros and cons


I would like to know  what are contract first and contract last. What are the pros and cons of each approach. When to use which one. Please advise
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Kanti PrasadCommented:

Contract-first is an implementation created from WSDL and Contract-last is where the WSDL and your XSD is created by a tool or java code than created by the developer and has no guarantee that the contract stays constant over time.

Here is some info
Ankit PareekOnline MarketingCommented:
contract-first is where you create the WSDL, and then you can create the implementation from this, and since the WSDL is your contract, this would be contract-first.
Simple, less time consuing, easy to use for those not aware with web services.
Also good approach to convert a legacy code in to WSDL web services
Its provide less control
If you change in service conde, WSDL will be change accordingly
time to time changes in WSDL not allowed

is where the WSDL is created from the source code, or implementation, so it will most likely be generated by a tool rather than created by the developer.

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gudii9Author Commented:
2.3.3. Reusability
Defining your schema in a separate file allows you to reuse that file in different scenarios. If you define an AirportCode in a file called airline.xsd, like so:
<simpleType name="AirportCode">
    <restriction base="string">
        <pattern value="[A-Z][A-Z][A-Z]"/>
You can reuse this definition in other schemas, or even WSDL files, using an import statement.
2.3.4. Versioning
Even though a contract must remain constant for as long as possible, they do need to be changed sometimes. In Java, this typically results in a new Java interface, such as AirlineService2, and a (new) implementation of that interface. Of course, the old service must be kept around, because there might be clients who have not migrated yet.
If using contract-first, we can have a looser coupling between contract and implementation. Such a looser coupling allows us to implement both versions of the contract in one class. We could, for instance, use an XSLT stylesheet to convert any "old-style" messages to the "new-style" messages.

i am bit unclear on above two points. why do the future changes happens and how it impacts implementation and how contract first is better in those scenarios?
please advise
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