The time it takes to prepare for the exam varies from person to person, based on their familiarity with Web Services.
Having prior experience is always a plus, however it is possible to clear this exam with proper study of all the exam objectives. One should try to avoid attempting the exam if he is not confident with all the exam objectives.
Here are the exam objectives:
XML Web Service Standards
SOAP 1.1 Web Service Standards
Describing and Publishing (WSDL and UDDI)
SOAP and XML Processing APIs (JAXP, JAXB, and SAAJ)
J2EE Web Services
Developing Web Services
General Design and Architecture
Endpoint Design and Architecture
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