Call a SOAP web service

Status

What other tools call it

Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3).

Background

When to use it

A Web Services Description Language (WSDL) file gives a machine-readable description of how a web service can be called, what parameters it expects and what data structures it returns.^[4] Apache Hop's Web services lookup transform loads the WSDL document from a given location and tries to fill in its input and output fields automatically.^[5] Apache Hop's Web services lookup transform lets the operation request name be entered by hand, because on occasion the WSDL gives back the wrong one.^[5] In Apache Hop's Web services lookup transform, the number of rows per call sets how many rows are sent with each WSDL call.^[5] Test a SOAP call on a handful of rows before running it over the whole table. (Meridian's view)

In SOAP 1.2, a SOAP fault is an element information item that contains fault information generated by a SOAP node.^[2] SOAP nodes are the physical or logical machines that transmit, forward, receive and process SOAP messages.^[1] Read fault elements into columns of their own, so a failed call is not loaded as if it were a result. (Meridian's view)

The method

SOAP Version 1.2 Part 1 defines, using XML technologies, an extensible messaging framework whose message construct can be exchanged over a variety of underlying protocols.^[2] SOAP consists of an envelope, which defines the message structure and how to process it, encoding rules for application-defined datatypes, and a convention for representing procedure calls and responses.^[1] SOAP originally stood for Simple Object Access Protocol, and version 1.2 of the standard dropped the acronym.^[1] The SOAP specification was maintained by the XML Protocol Working Group of the World Wide Web Consortium (W3C) until the group was closed on 10 July 2009.^[1] Version 1.1 of SOAP was published as a W3C Note on 8 May 2000, and version 1.2 became a W3C Recommendation on 24 June 2003.^[1]

WSDL 2.0 describes a web service at an abstract level in terms of the messages it sends and receives, and at a concrete level by bindings that give transport and wire format details.^[6] In WSDL 2.0, an operation associates a message exchange pattern with one or more messages, and an endpoint associates a network address with a binding.^[6] WSDL Version 2.0 Part 1: Core Language is a W3C Recommendation of 26 June 2007.^[6]

XML-RPC is a remote procedure calling protocol in which each message is an HTTP POST request with an XML body, and the value the procedure returns is formatted in XML.^[7] SOAP evolved as a successor of XML-RPC.^[1]

Compared with the alternatives

SOAP-based web application programming interfaces (APIs) mandate XML as the payload format, while web APIs in the Representational State Transfer (REST) style typically use JavaScript Object Notation (JSON) or XML.^[8][9][10] SOAP-based web APIs use XML validation, through the XML schemas provided with WSDL documents, to ensure structural message integrity.^[8]

Sources

1. [1]SOAP - Wikipediasecondary source
2. [2]SOAP Version 1.2 Part 1: Messaging Framework (Second Edition)standard
3. [3]XML - Wikipediasecondary source
4. [4]Web Services Description Language - Wikipediasecondary source
5. [5]Web services lookup | Apache Hopdocumentation
6. [6]Web Services Description Language (WSDL) Version 2.0 Part 1: Core Languagestandard
7. [7]XML-RPC Specificationstandard
8. [8]Web API - Wikipediasecondary source
9. [9]REST - Wikipediasecondary source
10. [10]JSON - Wikipediasecondary source