UDDI (Universal Description Discovery and Integration)
UDDI is a standard developed by a community of vendors across a diverse set of industries. It defines interfaces for registering as well as finding businesses and services in a XML registry. The Publisher API enables a business to store or update data about themselves in the registry. This data includes name, description, classification(s), and available Web services. In order to publish data to a registry, the business must first establish credentials with the registry owner. There are a number of publicly available registries, including ones operated by Microsoft and IBM. It is also possible to setup a private registry for internal enterprise applications or secure B2B applications. The Inquiry API is defined in terms of SOAP over HTTP and allows users to discover services of interest. Although not defined by the UDDI specification, it is becoming the industry best practice to define the Web service interface in WSDL.
WSDL (Web Services Definition Language)
This is analogous with the IDL (Interface Definition Language) from the CORBA/RMI distributed technologies. It defines the Web service, the operations it exposes (method name, parameter details), and most importantly, the service location. However, unlike CORBA and RMI, which used IIOP for transport mechanism, WSDL defines the supported transport mechanism for the given service. The most common of these is SOAP over HTTP.
For more information, see: Introduction to WSDL
Digital Signature
Digital Signature technology defines the mathematical algorithms for "signing" electronic data to create a legally binding transaction between the party that presents the data and the party that signs it. The signer generates a pair of cryptographic keys—a private key (for use in signing) and a public key (for use in verifying). The signer must publish the public key (usually done by requesting a digital certificate issued by a third-party that vouches for the validity of the key pair). The private key must remain in the possession of the signer and must not be compromised. The signer generates a hash of the original data, signs it with their private key, and sends it to the recipient for verification. The recipient can look up the corresponding digital certificate to ensure that the private key has not been compromised and then verify that the original message was not tampered with in transit. Digital signatures provide the following guarantees:
XML Signature
Digital Signature does not define a document structure for sending signed data—this is where the XML Signature specification comes into play. It defines an XML document structure for representing both the digital signature data as well as the original message that is signed. It also includes elements for defining the algorithm(s), message digests, public key for verification purposes, digital certificates, and much more.
For more information, see: XML-Signature Specification
SOAP-DSIG
The SOAP-DSIG specification brings the pieces together. SOAP defines the XML structure for distributed computing. XML signatures provide the XML structure for digital signatures. The SOAP-DSIG note defines how to represent an XML Signature within a SOAP RPC-style message.
For more information, see: SOAP-DSIG Note