Web Services 3

Question 1

simple, lightweight XML protocol for exchanging structured and typed information on the Web

Answer 1

SOAP

Question 2

Overall design goal: KISS

Answer 2

• Can be implemented in a weekend
• Stick to absolutely minimum of functionality

Question 3

Make it Modular and Extensible

Answer 3

• No application semantics and no transport semantics
• Think “XML datagram”

Question 4

SOAP Contains Four Parts

Answer 4

1. An extensible envelope expressing (mandatory)
2. A set of encoding rules for data (optional)
3. A Convention for representation RPC (optional)
4. A protocol binding to HTTP and HTTP-EF (optional)

Question 5

An extensible envelope expressing (mandatory)

Answer 5

• what features and services are represented in a message;
• who should deal with them,
• whether they are optional or mandatory.

Question 6

A set of encoding rules for data (optional)

Answer 6

• Exchange instances of application-defined data types and directed graphs
• Uniform model for serializing abstract data models that can not directly be expressed in XML schema

Question 7

A Convention for representation RPC (optional)

Answer 7

How to make calls and responses

Question 8

SOAP Example in HTTP

Answer 8

SOAP - HTTP BINDING
HTTP REQUEST
SOAP BODY
SOAP HEADER
SOAP ENVELOPE

Question 9

SOAP Example in SIP

Answer 9

SOAP - SIP Binding
SIP Request
SOAP Body
SOAP Envelope

Question 10

Session Initiation Protocol

Answer 10

a signaling protocol that enables the Voice Over Internet Protocol (VoIP) by defining the messages sent between endpoints and managing the actual elements of a call.

Question 11

HTTP

Answer 11

Used for transferring web content like HTML pages.

Question 12

TCP

Answer 12

Ensures reliable, ordered delivery of data packets.

Question 13

UDP

Answer 13

Provides fast but unreliable data transmission, commonly used for real-time applications like streaming and gaming.

Question 14

• Connection-oriented, ensuring reliable, ordered data transmission.
• Performs error-checking and retransmission.
• Higher overhead, suitable for applications requiring reliability like web browsing and file transfer.

Answer 14

TCP

Question 15

• Connectionless, offering faster but less reliable transmission.
• Does not guarantee packet order or error recovery.
• Lower overhead, preferred for real-time applications like streaming, gaming, and VoIP.

Answer 15

UDP

Question 16

Note Again: SOAP is a Protocol!

Answer 16

a. What does this mean?
* It is not a distributed object system
* It is not an RPC system
* It is not even a Web application

b. Your application decides what your application is!
* You can build a tightly coupled system
…or…
* You can build a loosely coupled system

Question 17

Evolvability

Answer 17

ability of a system to adapt and change easily over time to meet new needs or challenges

Question 18

How are features and services deployed in the Web?

Answer 18

• Often by extending existing applications
• Spreading from in the small to the large over time

Question 19

This means that SOAP is Designed for Evolvability:

Answer 19

• Applications have different capabilities at all times
• We have to support this

Question 20

This requires that SOAP is Designed for Evolvability:

Answer 20

• Applications supporting a particular feature or service should be able to employ this with no prior agreement;
• Applications can require that the other party either understand and abide by the new feature or service or abort the operation

Question 21

Why Not Roll My Own XML Protocol?

Answer 21

• SOAP allows you to define your particular feature or service in such a way that it can co-exist with other features and services within a SOAP message
• What is a feature or a service?
  a. What is a feature or a service?
  b. Authentication service
  c. Payment service
  d. Security service
  e. Transaction management service
  f. Privacy service
• Not owning the message means easier deployment and better interoperability

Question 22

What is a feature or a service?

Answer 22

1. Authentication service
2. Payment service
3. Security service
4. Transaction management service
5. Privacy service

Question 23

Interoperability

Answer 23

refers to the ability of different systems, devices, or components to seamlessly work together, exchange data, and communicate effectively, regardless of their differences in technology, platforms, or protocols.

Question 24

is the intersection of features and service supported by two or more communicating peers

Answer 24

Interoperability

Question 25

refers to the capability of a system to easily add new features, functionalities, or capabilities without significantly altering its existing structure or core functionality.

Answer 25

Extensibility

Question 26

Extensibility

Answer 26

Cost per new feature/service increases over time

Question 27

Evolvability

Answer 27

Cost per new feature/service is flat

Question 28

Composability

Answer 28

refers to the ability of individual components or elements within a system to be combined or arranged in various ways to create new, larger systems or applications. It emphasizes modularity and flexibility, allowing for the construction of complex systems from simpler, interchangeable parts.

Question 29

XML meaning

Answer 29

Extensible Markup Language

Question 30

* multiple features and services can exist simultaneously within the same message * Allows for independent features to co-exist

Answer 30

Vertical Composability

Question 31

* features and services within a message can be intended for different recipients. * Allows for intermediaries

Answer 31

Horizontal

Question 32

intermediaries in horizontal composability

Answer 32

1. authentication 2. actor 3. transaction 4. payment

Question 33

Modularity through XML Namespaces

Answer 33

1. The SOAP envelope namespace 2. The SOAP encoding namespace 3. Separate namespaces help enforce modularity 4. SOAP Envelope Schema provides formal definition of Envelope

Question 34

RPC meaning

Answer 34

Remote Procedure Call

Question 35

SOAP Envelope

Answer 35

1. A SOAP envelope defines a SOAP message 2. messages are one-way transmissions 3. Messages are routed along a "message path" 4. Envelopes can be nested

Question 36

Allows for processing at one or more intermediate nodes in addition to the ultimate destination node. (True or False)

Answer 36

True

Question 37

a SOAP processor and is identified by a URI

Answer 37

node

Question 38

SOAP Headers

Answer 38

* Allows for modular addition of features and services * Open-ended set of headers * Authentication, privacy, security etc. etc. * Can address any SOAP processor using the "actor" attribute * Can be optional/mandatory using the "mustUnderstand" attribute

Question 39

Semantics of SOAP Headers

Answer 39

1. Contract between sender and recipient/actor 2. allows differengt types of negotiation (take it or leave it; lets talk about it can be built on top) 3. And for different settings (server dictated, peer-to-peer, dictated by third party)

Question 40

has a special URI assigned to it

Answer 40

next hop

Question 41

is the default destination for a header

Answer 41

end

Question 42

is the destination for the body

Answer 42

end

Question 43

attribute is a generalization of the HTTP Connection header field

Answer 43

actor

Question 44

The SOAP actor Attribute

Answer 44

Instead of hop-by-hop vs. end-to-end, the actor attribute can address any SOAP processor because it is a URI

Question 45

URI meaning

Answer 45

Uniform Resource Identifier

Question 46

* " is the same as "mandatory" in the HTTP Extension Framework * This allows old applications to gracefully fail on services that they do not understand

Answer 46

mustUnderstand

Question 47

* Special case of header * Default contract between sender and ultimate recipient * Different from HTTP's header/body separation * Defined as a header with attributes set to: * Implicit mustUnderstand attribute is always "yes" * Implicit actor attribute is always "the end"

Answer 47

SOAP Body

Question 48

* Bad experiences with version numbers in decentralized environments * Extremely confusing in HTTP – whole RFC on the topic * Typical uses of number based "versioning" * Backwards compatible (minor version number) * Backwards incompatible (major version number * SOAP supports "minor" versioning within the envelope using header and body elements * The SOAP composability model ("WYSIWYG on the wire") * The SOAP Envelope Namespace URI defines the "major" of the SOAP envelope * Changing Namespace URI is equivalent to change major version number * Possible to negotiate major versioning change using SOAP header * Equivalent to the HTTP Upgrade header field | manages changes in communication protocols. ## Footnote It's like making sure everyone's speaking the same language, even as that language evolves. Version numbers help keep track of these changes, ensuring compatibility between different systems.

Answer 48

SOAP Versioning Model

Question 49

* "Binary" can in fact mean any data that is to be tunneled through SOAP * Encrypted data, images, XML documents, SOAP envelopes as data * Can be carried in two ways * Within the envelope as binary blob * Referenced from within the SOAP envelope * References can point to anything including * MIME multipart, HTTP accessible resources etc. * Integrity can be obtained through manifest | "binary" data in SOAP, we mean any non-textual information. ## Footnote This data can be included directly in the SOAP message or referenced from elsewhere. To make sure everything is secure and intact, we can use a manifest to verify the integrity of the data.

Answer 49

SOAP and "Binary" Data

Question 50

* The purpose of the HTTP protocol binding is two-fold * To ensure that SOAP is carried in a way that is consistent with HTTP’s message model * Intent is not to break HTTP * To indicate to HTTP servers that this is a SOAP message * Allows HTTP servers to act on a SOAP message without knowing SOAP * Binding only works for HTTP POST requests * SOAP intermediary is not the same as HTTP intermediary * Only HTTP origin server can be SOAP intermediary | binding SOAP to HTTP means ensures that SOAP messages play in the rules ## Footnote It helps HTTP servers recognize and handle SOAP messages appropriately, particularly when they're sent as HTTP POST requests. However, it's important to distinguish between SOAP and HTTP intermediaries, as their roles and capabilities differ.

Answer 50

Binding to HTTP

Question 51

* Use HTTP POST request method name * Use the SOAPAction HTTP header field * It cannot be computed – the sender must know * It should indicate the intent – not the destination * SOAP request doesn't require SOAP response ## Footnote * You use the POST method. * You include a SOAPAction header to specify what action the SOAP service should perform. * The sender needs to know what action to request. * The SOAPAction field indicates the intended action, not necessarily where the message should go. * And finally, while you're asking the SOAP service to do something, you might not always get a response back.

Answer 51

HTTP Request

Question 52

* Successful responses can 2xx status codes (It's like getting a thumbs-up or a green light.) * All 3xx, 4xx, and 5xx status codes work as normal * SOAP faults must use 500 status code * SOAP response doesn't require SOAP request * Response can in fact be empty ## Footnote * If everything's okay, you get a status code starting with "2." * If there's a problem with the request, you might get a status code starting with "3," "4," or "5." * If there's a SOAP-specific issue, like a fault, you'll likely get a 500 status code. * You might receive a SOAP response even without sending a SOAP request. * Sometimes, the server might not have anything to say, and the response can be empty.

Answer 52

HTTP Response

Question 53

Purpose of SOAP Encoding (1)

Answer 53

Given a schema in any notation consistent with the data model defined by SOAP, a schema for an XML grammar may be constructed ## Footnote SOAP encoding provides a way to structure data in XML format, ensuring consistency and making it easier for different systems to understand and exchange information effectively. It's like having a set of rules for organizing information so that everyone is on the same page.

Question 54

Purpose of SOAP Encoding (2)

Answer 54

Given a type-system schema and a particular graph of values conforming to that schema, an XML instance may be constructed. ## Footnote SOAP encoding helps us take different types of data, organize them according to a set of rules (schema), and convert them into a structured XML format that follows those rules.

Question 55

Basic Rules

Answer 55

1. All values are represented as element content 2. An element may be "independent" (top level of serialization) or "embedded" (everything else) 3. Values can be single-reference or multi-reference 4. A multi-reference value is represented as the content of an independent element. It has an unqualified attribute named "id" and of type "ID". 5. An accessor can point to a multi-reference value with a local, unqualified attribute named "href" and of type "uri-reference“ 6. The root attribute can be used to indicate roots that are not true roots in a graph

Question 56

Purpose of SOAP Encoding (3)

Answer 56

Given an XML instance produced in accordance with these rules, and given also the original schema, a copy of the original value graph may be constructed. ## Footnote SOAP encoding ensures that data is structured correctly in XML format according to specific rules (schema). This structured XML data can then be used to reconstruct the original data graph, providing a way to represent and exchange complex information in a standardized manner.

Question 57

Indicating the Type

Answer 57

* For each element containing a value, the type of the value is represented by at least one of the following conditions: * The containing element instance contains an xsi:type attribute, * The containing element instance is itself contained within an element containing a (possibly defaulted) SOAP-ENC:arrayType attribute or * The name of the element bears a definite relation to the type, that type then determinable from a schema.

Question 58

* A "simple type" is a class of simple values * SOAP uses all the types found in the section "Built-in data types" of "XML Schema Part 2: Datatypes" * A simple value is represented as character data, that is, without any sub-elements ## Footnote * simple type refers to basic values, like numbers or words, which are represented directly as text in SOAP messages. * These values are straightforward and don't have any internal structure or sub-elements.

Answer 58

Simple Types

Question 59

* A “compound” type is a class of compound values * Each related value is potentially distinguished by a role name, ordinal or both (accessor) * Supports traditional types like structs and arrays * Supports nodes with with many distinct accessors, some of which occur more than once * Preserves order but doesn't require ordering distinction in the underlying data model

Answer 59

Compund Type ## Footnote * compound types represent more complex values that consist of multiple related parts. * These parts can be identified by names or positions, and they support familiar data structures like structs and arrays. * Compound types allow for organizing data in a structured way while preserving the order of the information.

Question 60

in which ***accessor name*** is the only distinction among member values, and no accessor has the same name as any other

Answer 60

Struct Compound Type ## Footnote struct compound type is like a set of labeled boxes, where each box holds a different piece of information, and each label is unique. You can think of it as a way of organizing data into distinct categories based on their names.

Question 61

A compound value in which ***ordinal position*** serves as the only distinction among member values

Answer 61

Array Compound Type ## Footnote array compound type is like a list of items where each item is identified by its position in the list. You can think of it as a way of organizing data into a sequential order, where each piece is numbered according to its place in the sequence.

Question 62

A compound value with a mixture of accessors distinguished by name and accessors distinguished by both name and ordinal position

Answer 62

General Compound Type ## Footnote general compound type is like a mixture of labeled boxes and numbered boxes. Some pieces of information have unique names, while others are simply numbered based on their position. It's a flexible way of organizing data, allowing for different ways to identify and access the information within the compound value.

Question 63

Serializing Relationships

Answer 63

* The root element of the serialization serves only as lexical container. * Elements can reflect arcs or nodes * Independent elements always reflect nodes * Embedded elements always reflect arcs * Element names correspond to node or arc labels * Arcs are always encoded as embedded elements ## Footnote * The main element is like a box holding everything. * Elements can represent either individual data points (nodes) or the connections between them (arcs). * Node elements stand alone, while arc elements are nested within node elements. * The names of elements correspond to the labels or identifiers of the data points they represent. * Arcs, representing connections, are always shown as part of the data points they connect.

Question 64

relationship is expressed by simple containment. For example, if a student attends a course, the canonical XML looks like

Answer 64

1:1 Relationships

Question 66

A 1:many relationship is expressed by multiple elements for the 1:many direction or single element for the many:1 direction.

Answer 66

1:n and n:1 Relationships

Question 67

is expressed by using references in both directions.

Answer 67

m:n Relationships

Question 68

SOAP and RPC

Answer 68

* A method invocation is modeled as a struct * A method response is modeled as a struct * Struct contains an accessor for each [in] or [in/out] or [out] parameter. * The request struct is both named and typed identically to the method name. * The response struct name is not important * The first accessor is the return value followed by the parameters in the same order as in the method signature ## Footnote SOAP and RPC use structured data (structs) to represent method invocations and responses. These structs contain accessors for each parameter of the method, following a specific naming convention for the request struct and maintaining the order of parameters as in the method signature.