SOAP Encoding, cont.

Transcription

1 Data Encoding Knowing that two distributed systems support packaging and processing data with SOAP is not enough to get the two systems to interoperate. You must also define how the payload of the package (the data) is formatted so that both parties can understand the data. How the data is translated to XML is called data encoding. Data encoding involves defining the organization of the data structure, the type of data that can be encoded, and the value of the data. Both communicating parties must know how the data is encoded. How the data is encoded in XML (the encoding style) is not restricted by the SOAP specification. You just need to make sure that both the sender and receiver know what encoding style is being used and how to translate it.

2 SOAP Encoding Part 2, section 3 of the SOAP 1.2 specification (section 5 in SOAP 1.1) defines a style of encoding that may be used which provides support for RPC (Remote Procedure Call) style messaging. This encoding style is commonly referred to as SOAP Encoding or SOAP Section 5 Encoding. The WS-I BP strictly prohibits its use because it has been a major source of confusion and interoperability problems. Specifying the encoding style as SOAP Encoding does not provide enough information for SOAP nodes to know how to encode and decode the data in a SOAP message. That is because nothing in SOAP Encoding forces the use of a specific typing system for data. SOAP Encoding describes a structure for the data but leaves describing the types of data up to the implementation. Most use XML Schema data types.

3 SOAP Encoding, cont. SOAP experts suggest that data in SOAP messages be structured and typed using XML Schema Part 1: Structures and XML Schema Part 2: Datatypes because XML Schema is perceived as having a better type system and better interoperability than SOAP Encoding. SOAP Encoding was developed while the XML Schema was in draft form and before XML Schema supported complex types, which allow you to model data like Java classes. Additionally, XML Schema structures data in a tree form, which is not as flexible as the object graph form that SOAP Encoding uses. The data structure used by SOAP Encoding is called the SOAP Data Model.

4 XML Tree Structure <A> <B> <D></D> </B> <C> <E></E> <F></F> </C> </A> parses to D B A E C F

5 SOAP Data Model Represents data as a graph of nodes connected by directional edges. Nodes represent a piece of encoded data, which the SOAP specification refers to as values, and the edges are referred to as labels Bill Eva name streetnumber name Person address Address address Person gender state city gender male SC Hopkins female

6 SOAP Data Model, cont. A simple value is a node with no outgoing edges, in other words, a node with no arrows (edges) pointing from it to another node, only arrows pointing from other nodes to it. A compound value is just the opposite; it is a node with outgoing edges. A compound value may reference simple values or other compound values. Values with multiple incoming edges are called multireference values or multirefs (Address in the previous slide). Simple values in Java are java.lang.string, int, float, long, double, byte, and char. Compound values in Java are arrays, classes that are defined by the JDK, and any classes that you create.

7 SOAP Data Model, cont. When the outgoing edges of a compound value have names (as in the previous figure), the node is referred to as a struct (a class in Java or struct in C/C++). A compound value with outgoing edges that aren t named is called an array (like an array in Java or C/C++). A compound value may represent either an array or a struct, but not both. The mechanism that is used to refer to the values within a compound value is called an accessor. In the case of a Java class, the fields within the class are accessed via the field names (labels in the SOAP Data Model). With a Java array, the data the array holds are accessed by indicating an ordinal position. And with a hash table the data is accessed using keys to an associative array.

8 SOAP Data Model, cont. Address from the previous figure coded in Java: class Address { int streetnumber; String city; String state; } public Address(int streetnumber, String city, String state) { this.streetnumber = streetnumber; this.city = city; this.state = state; }

9 SOAP Data Model, cont. Person from previous figure coded in Java: class Person { string name; string gender; Address address; public Person(String name, String gender, Address address) { this.name = name; this.gender = gender; this.address = address; } } Address home = new Address(1000, Hopkins, SC ); Person Bill = new Person( Bill, male, home); Person Eva = new Person( Eva, female, home);

10 SOAP Encoding, cont. The purpose of SOAP Encoding is to describe a standard convention for taking a SOAP Data Model and writing it out as XML. The resultant XML may be used in a SOAP header block or the SOAP Body. SOAP Encoding defines a narrower set of rules than that provided by XML such that SOAP applications will know how to process data using the SOAP Data Model. The industry trend is to use XML Schema instead of SOAP Encoding, however SOAP Encoding does provide some benefits of XML Schema like shared references to pieces of data and a common definition of an array, which is a data structure that is found in most all programming languages.

11 SOAP encodingstyle Attribute Used to specify a URI that identifies the encoding style (rules) you are using to serialize and deserialize data elements. The SOAP 1.2 specification states that the encodingstyle attribute can appear on only header blocks or their children, the immediate child of the Body element or its children, except the Fault element, and the immediate child of a Fault Detail element or its children. The encodingstyle attribute cannot be used on any other elements. When used, the encodingstyle attribute applies encoding rules to the element it appears on and all of its children, unless a child also contains an encodingstyle attribute.

12 SOAP encodingstyle Attribute The SOAP specification indicates no default value for the encoding style therefore, if the encodingstyle attribute is omitted or assigned an empty value ( ), then no claims and thus no assumptions are to be made of the encoding in use. The values that can be assigned to the encodingstyle attribute are: - Indicates that you are using SOAP Encoding. - Has the same affect as setting the encodingstyle attribute to an empty value ( ). A custom value (like that indicates some other encoding style is in use. The WS-I BP prohibits the use of encodingstyle.

13 SOAP encodingstyle Attribute <soap:envelope xmlns:soap= xmlns:myns= > <soap:body> <myns:person soap:encodingstyle= > <myns:name>bill</myns:name> <myns:gender>male</myns:gender> <myns:address> <myns:streetnumber>1000</myns:streetnumber> <myns:city>hopkins</myns:city> <myns:state>sc</myns:state> </myns:address> </myns:person> <myns:person soap:encodingstyle = > </myns:person> </soap:body> </soap:envelope>

14 Specifying Data Types The type of data that each XML element contains must be specified for a SOAP receiver to fully understand the data in a SOAP message. One three ways can be used to specify the data type for an application-specific XML element in a SOAP message: 1) The XML element can include the XML Schema attribute called type with an assigned value equal to one of the valid type identifiers specified in XML Schema Part 2: Datatypes. 2) The XML element can include the SOAP Encoding itemtype attribute, which restricts all child elements of that element to the data type specified by the assigned value. 3) The XML element names can be associated with data types defined by an associated XML schema.

15 Specifying Data Types -- xsi:type <soap:envelope xmlns:soap= xmlns:myns= xmlns:xsi= xmlns:xsd= > <soap:body> <myns:person soap:encodingstyle= > <myns:name xsi:type= xsd:string >Bill</myNs:name> <myns:gender xsi:type= xsd:string >male</myns:gender> <myns:address id= 1 > <myns:streetnumber xsi:type= xsd:int >1000 </myns:streetnumber> <myns:city xsi:type= xsd:string >Hopkins</myNs:city> <myns:state xsi:type= xsd:string >SC</myNs:state> </myns:address> </myns:person> </soap:body> </soap:envelope>

16 Specifying Data Types - soapenc:itemtype <soap:envelope xmlns:soap= xmlns:soapenc= xmlns:xsd= xmlns:myns= > <soap:body> <myns:numbers soapenc:itemtype= xsd:int soapenc:arraysize= 3 soap:encodingstyle= > <myns:number>123456</myns:number> <myns:number>098765</myns:number> <myns:number>675849</myns:number> </myns:numbers> </soap:body> </soap:envelope>

17 Specifying Data Types - XML Schema <soap:envelope xmlns:soap=" xmlns:myns= > <soap:body> <myns:person soap:encodingstyle = > <myns:name>bill</myns:name> <myns:gender>male</myns:gender> <myns:address id= 1 > <myns:streetnumber>1000</myns:streetnumber> <myns:city>hopkins</myns:city> <myns:state>sc</myns:state> </myns:address> </myns:person> </soap:body> </soap:envelope>