23
CHAPTER II LITERATURE REVIEW
2.1 Definition System
The system is an interconnected group of components and works together to achieve a common goal by accepting inputs and producing outputs in an orderly
process of transformation OBrien, 2005.
2.2 System Characteristics
A good system has the following characteristics Mcleod and Schell, 2001: 1. Flexible
Although an effective system is a system that structured and well organized, but should be flexible enough to be more easily adapted to the
circumstances that change frequently. 2. Easily Adapted
A good system should also be quickly and easily adapted to new conditions without changing the old system and interfere with its primary
function. 3. Systematic
In order to function effectively, the existing system should be logical and systematic, that is, the system created will not complicate the work
activities that already exist. 4. Functional
An effective system must be able to help achieve its intended purpose. 5. Simple
24 A system should be simpler so it is more easily understood and
implemented. 6. Optimal resource utilization
Well-designed system will make use of the resources of the organization can be optimized utilization.
2.3 Web Service Web service
is a method of communication between two electronic devices over a network.
The W3C defines a Web service as a software system designed to
support interoperable machine-to-machine interaction over a network. It has an interface described in a machine
– process able format specifically Web Services Description Language
WSDL. Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed
using HTTP with an XML serialization in conjunction with other Web-related standards[6].
The Web Services Description Language WSDL, pronounced wiz-del
is an XML-based language that provides a model for describing Web services. The WSDL defines services as collections of network endpoints, or ports. The
WSDL specification provides an XML format for documents for this purpose. The abstract definitions of ports and messages are separated from their concrete use or
instance, allowing the reuse of these definitions [6]. A port is defined by associating a network address with a reusable binding,
and a collection of ports defines a service. Messages are abstract descriptions of
25 the data being exchanged, and port types are abstract collections of supported
operations. The concrete protocol and data format specifications for a particular port type constitutes a reusable binding, where the operations and messages are
then bound to a concrete network protocol and message format. In this way, WSDL describes the public interface to the Web service.
Figure 2.3.1 Example of WSDL
ServiceService: The service can be thought of as a container for a set of system
functions that have been exposed to the Web-based protocols.
PortEndpoint: The portendpoint does nothing more than define the address or
connection point to a Web service. It is typically represented by a simple HTTP URL string.
26
BindingBinding: The binding specifies the interface as well as defining the
SOAP binding style RPCDocument and transport SOAP Protocol. The binding section also defines the operations.
PortTypeInterface: The portType element, renamed to interface in WSDL
2.0, defines a Web service, the operations that can be performed, and the messages that are used to perform the operation.
OperationOperation:
Each operation can be compared to a method or function call in a traditional programming language. Here the SOAP actions are defined
and the way the message is encoded, for example, literal.
MessageN.A.: Typically, a message corresponds to an operation. The message
contains the information needed to perform the operation. Each message consists of one or more logical parts. Each part is associated with a message-typing
attribute. The message name attribute provides a unique name among all messages. The part name attribute provides a unique name among all the parts of
the enclosing message. Parts are a description of the logical content of a message. In RPC binding, a binding may reference the name of a part in order to specify
binding-specific information about the part. A part may represent a parameter in the message; the bindings define the actual meaning of the part. Messages were
removed in WSDL 2.0, in which XML schema types for defining bodies of inputs, outputs and faults are referred to simply and directly.
Extensible Markup Language XML is a set of rules for encoding documents
in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards [6].
27 XMLs design goals emphasize simplicity, generality, and usability over the
Internet. It is a textual data format with strong support via Unicode for the languages of the world. Although the design of XML focuses on documents, it is
widely used for the representation of arbitrary data structures, for example in web services.
Figure 2.3.2 Example of xml
The material in this section is based on the XML Specification. This is not an exhaustive list of all the constructs which appear in XML; it provides an
introduction to the key constructs most often encountered in day-to-day use.
Unicode Character
By definition, an XML document is a string of characters. Almost every legal Unicode character may appear in an XML document.
Processor and Application
The processor analyzes the markup and passes structured information to an application. The specification places requirements on what an XML processor
28 must do and not do, but the application is outside its scope. The processor as the
specification calls it is often referred to colloquially as an XML parser [6].
Markup and Content
The characters which make up an XML document are divided into markup and content. Markup and content may be distinguished by the application of simple
syntactic rules. All strings which constitute markup either begin with the character and end with a , or begin with the character and end with a ;. Strings
of characters which are not markup are content.
Tag
A markup construct that begins with and ends with . Tags come in three flavors: start-tags, for example section, end-tags, for example section, and
empty-element tags, for example line-break . Element
Element is a logical component of a document which either begins with a start-tag and ends with a matching end-tag, or consists only of an empty-element tag. The
characters between the start- and end-tags, if any, are the elements content, and may contain markup, including other elements, which are called child elements.
An example of an element is GreetingHello, world.Greeting see hello world. Another is line-break .
Attribute
A markup construct consisting of a namevalue pair that exists within a start-tag or empty-element tag. In the example below the element img has two attributes, src
and alt: img src=madonna.jpg alt=Foligno Madonna, by Raphael . Another
29 example would be step number=3Connect A to B.step where the name of
the attribute is number and the value is 3.
SOAP , originally defined as Simple Object Access Protocol, is a protocol
specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on Extensible Markup Language XML
for its message format, and usually relies on other Application Layer protocols, most notably Remote Procedure Call RPC and Hypertext Transfer Protocol
HTTP, for message negotiation and transmission. SOAP can form the foundation layer of a web services protocol stack, providing a basic messaging
framework upon which web services can be built. This XML based protocol consists of three parts: an envelope, which defines what is in the message and how
to process it, a set of encoding rules for expressing instances of application- defined data types, and a convention for representing procedure calls and
responses [6].
2.4 Authentication