Web Service Architecture Quiz

Study Notes

A web service consists of three components: service requester, service provider, and service registry.
Basic infrastructure to implement a web service includes:
- A way to communicate (SOAP - Simple Object Access Protocol).
- A way to describe the service (WSDL - Web Service Description Language).
- A name and directory service (UDDI - Universal Description, Discovery, and Integration).

A common syntax is needed for all specifications, provided by XML.
There must be a mechanism for remote sites to interact, including:
- Common data format for messaging.
- Convention for interactions (messaging or RPC).
- Bindings for mapping messages into a transport protocol.

SOAP was initiated by W3C in 1999 and is used for message exchanges.
SOAP covers four main areas:
- Message format for one-way communication.
- Description of how to transport the message through the web or email.
- Rules for processing a SOAP message.
- Conventions for turning an RPC call into a SOAP message and back.

A SOAP message consists of an envelope, header, and body.
The header and body are divided into blocks.
The header is optional and the body is mandatory.
The header is for infrastructure-level data, and the body is for application-level data.

In SOAP 1.1, the fault element has four elements: fault code, fault string, fault actor, and detail.
In SOAP 1.2, the fault element has two mandatory sub-elements: Code and Reason, and may contain Node, Role, and Detail elements.

SOAP specifies how messages must be processed, including how header entries must be processed.
Each SOAP node looks at the role associated with each part of the message.
Roles can be none, next, or ultimateReceiver.
The mustUnderstand attribute determines whether it is mandatory to process the header.

HTTP is used for exchanging documents and is almost like email.
Request methods include GET, POST, PUT, and DELETE.
The server is expected to convert the data into a MIME type specified in the request.

A binding of SOAP to a transport protocol is a description of how a SOAP message is to be sent using that protocol.
The typical binding for SOAP is HTTP.
SOAP can use GET or POST, but POST is typically used.### SOAP Basics
SOAP provides mechanisms for encapsulating messages into an XML document.
It maps the XML document to a SOAP message and turns it into an HTTP request.
SOAP transforms RPC calls into SOAP messages.
It has simple rules on how to process a SOAP message (which became more precise and comprehensive in v1.2 of the specification).

SOAP takes advantage of XML standards to resolve data representation and serialization problems.
It uses XML Schema to represent data and data structures.
It relies on XML for serializing data for transfer.
SOAP can take advantage of new XML standards by indicating what schema and encoding is used as part of the SOAP message.

SOAP is a simple protocol intended for transferring data from one middleware platform to another.
Current specifications are tied to RPC and HTTP.
Despite its claims to be open, SOAP is designed to be platform-independent.