Selecting Services for Web Applications The Open Hypermedia Case by localgirl

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									Selecting Services for Web Applications: The Open Hypermedia Case

Nikos Karousos, Manolis Tzagarakis, Nicolas Koumbarou

Dept. of Computer Engineering & Informatics University of Patras &

Research Academic Computer Technology Institute

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Introduction
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Popularity of the Web
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The need for effective information management systems proportionally increases. Web development, requires services like
information organization, authoring, versioning, annotation, sophisticated backtracking, information restructuring and similar services.

The deployment of a variety of hypermedia functionality into web projects will be valuable.
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Introduction
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Web engineers have already paid great attention to the web application development procedure. The Open Hypermedia Community has not yet:
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BUT
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A standardized a methodology.

A set of tools that can provide web developers to a quick and simple way to include Hypermedia functionality into their web applications

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Moreover, OHSs have not reached a satisfactory level of publicity and the Hypermedia service discovery issue still remains unaddressed

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Introduction
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This paper proposes a framework for enabling web developers to use hypermedia services into their applications.
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We study the design of both a Hypermedia Service Discovery Mechanism and a set of tools, in order to create a web developer support framework. We address the web developers’ needs and requirements concerning searching, selecting and using hypermedia services.

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A, B, C Levels of Work: Focus on C Level.
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Service Oriented Web Development
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The network-intensive nature of web applications means that these applications rely heavily on services that provide the required functionalities. The creation of a Web application usually demands the remote usage, or the integration of foreign services into the specified Web Project. Researchers in the area of WE have already approached this requirement from multiple scientific sides, including system architecture, productivity, economics, security and performance

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Service Oriented Web Development
From the developer’s perspective: When a developer intends to use foreign services to his application, he:
a)

b)

searches for the appropriate service through the network understands the exported interface and the way the service operates, implements the required communication protocol into the application in order to be able to request servicess encapsulates the adopted service as a set of functions that can be used by his application.
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c)

d)

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Developers’ requirements
1. 2.

3.
4. 5. 6.

Briefly,

A methodology for easy discovering services should be considered. The service should carry self-descriptive meta-information. Trust, security & reliability The existence of a driver that makes the usage of the service into the application, as simple as possible. The simplicity of the functions (of the service). Low maintenance cost, since a simple change of a complicated function will require large amount of changes in the integrated application.

a web developer needs to have a support framework which will provide easy-to-find, easy-to-understand and easy-to-use 3rd party services into his applications.
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Open Hypermedia Systems and the Web
Service oriented approach
Component Based Open Hypermedia Systems (CB-OHSs) & service oriented systems, Multiple Open Services project, Widely adopted concept of Structural Computing.

Web Integration efforts
Microcosm, with the Distributed Link Service (DLS), DHM, with DHM/WWW, Chimera etc.

Web service aproach
Babylon Web Service, SoFAR

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Why hypermedia systems are not used efficiently in the web development?
1. 2. 3.

4. 5.

Low publicity High complexity of using a hypermedia system A web developer who wants to use only one hypermedia service is indebted to get and have access (and to pay) for all the OHS usability. That, is ought in high connectedness between all components of the Hypermedia system Web integrations are usually ad-hoc implementations There aren’t any established methodologies or mechanisms for finding services in order to help web developers locating and using Hypermedia services into their applications.

The Hypermedia community creates diverse services and the web community benefits from these services and the structuring facilities offered by they provide.

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Service Discovery: Definition
The procedure of locating (inside or outside the network) the sources where information about servers can be found, querying these sources for available servers and matching the providing services of these servers with the user needs. Service discovery is completed when the requester is provided with the required server access information.

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Service Discovery: Related Work
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Server Information Management (SIM). Hypermedia Resource Descriptors (HRD). Web Services: Universal Description, Discovery and Integration of Web Services – (UDDI) CORBA: internal naming and discovery mechanism Open Hypermedia Protocol (OHP) contains aspects of functionality, that can help a client to discover all the services of a specified hypermedia server.
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Service Discovery: Architecture
Centralized Service Discovery
(e.g. UDDI) Drawbacks
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Fully dependent on one server

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QoS

Distributed Service Discovery
Drawbacks
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Complexity, security, latency of response time, etc. Maintenance of information distributed from a server directory to other directories.

P2P Service Discovery Hybrid approach of Service Discovery

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Service Discovery: Architecture
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Choosing the Appropriate Hypermedia Service Discovery Architecture
 Open

Hypermedia Systems do not consist of a large set of structure/link servers.  No hypermedia service discovery mechanism has yet been adopted.
Simple Centralized Hypermedia Service Discovery Mechanism This mechanism has to be extendable in order to be able to support a future transformation to a distributed or a hybrid service discovery system
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Introspection Capabilities of OHSs
A hypermedia system should be aware of all provided hypermedia services and how those can be invoked. A Hypermedia Service Description Language (HSDL) should be defined. This language can be based on emerging standardized markup languages, such as the Web Service Description Language (WSDL) and the Resource Description Framework (RDF), or it can be a new XML-based adhoc language

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Introspection Capabilities of OHSs
HSDL should be structured in a standard way and should include the following information:
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Service General Information. Service name, Service provider, Service scope, Structural specific information such as the Hypermedia domain (e.g. spatial) etc. Service Location and Access Information. Host and Port (or other location information), Communication Protocol(s) between client and Hypermedia server. Service Interface Information. Available Operations: Functions that can be called remotely from a client and can return a result. Data types that are passed or returned as function parameters. Service Behavior Information. Behavior of the Hypermedia server, after each request, Dependences between the server operations. Service Comments. By the developer
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Hypermedia Service Registry
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Registry Fields Hypermedia Owner InformationRegistry Service

Owner Name, Address, URL, etc. OHS Information OHS Name, OHS Description OHS Access Point Domain Information Domain Type Service Information Service Name, Service Description Required Communication Protocol Service Status - Service Location - HSDL Location Registry Information Registry Unique Name / ID Register Date, Duration, Description, etc.
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Hypermedia Service Query Language
A developer, who wants to use a hypermedia service into his application, must be able to search and locate services using a service query language. This language should be based on a common used communication protocol and must be able to be used by both humans and applications. Then, the hypermedia directory system will be a service by itself that will respond to searching requests in a standard common protocol. The query result could be a list of hypermedia service registries that matches all the requested criteria.

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Hypermedia Service Discovery Usability
Aiming to the growing usage of the OHSs, the discovery mechanism has to be available and easy to use by both humans and computers. One or more hypermedia directory web interfaces should be created.
Visual representation tools. - Service classification. - Tree-views with multiple perspectives.

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Discovering Hypermedia services: a step-by-step example
Web Developer
6. Establishing Service Communication

Hypermedia Server
5. Selecting (Getting HSDL File) 1. Requesting

4. Resulting Services 2. HSQL

HS Directory

Registration

HS Directory Interface
3. Results in XML

Hypermedia Service Discovery Mechanism

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Additional Tools
Hypermedia Services Exploring Tools Specific scope
Giving an OHS access point to the developers, an application that allows the visual exploration of available services of a particular hypermedia system should be available.

Global scope
A more complicated tool, which allows the navigation through all the available services of the hypermedia systems should be provided. Facilitates the understanding of the entire hypermedia system.

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Additional Tools
Communication Protocol Awareness
The developer should not worry about the communication protocol that has to be used in order to communicate with a specific hypermedia server.

Therefore:
approaches such as the Simple Object Access Protocol (SOAP) should be adopted, or the ability of dynamically locating and loading protocols – at run time -should be investigated. When the discovery mechanism returns a list of matched registry records, for each selected service that uses a well-known communication protocol, the required protocol access information will also be provided.
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Additional Tools
Automatic Client Skeleton Creation
Tools for automatic generation of the client communication layer should be developed. Some significant propositions have been made in this issue. In “Construct”, the developer is able to use tools for the automatic creation of skeleton code from a UML diagram or an IDL specification of a service. If a standardized hypermedia service description language was available then some more sophisticated and effective automatic client creation tools could be created.

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Future Work
Below are presented the future steps that must be followed in order to achieve the target goal:
Definition of the service registry record. Implementation of the first registry directory. Web – based directory interface creation. Definition of the HSDL. Applying Web Service in association with SOAP.

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Conclusions
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Hypermedia community can help and offer services that emerge as a result from system and domain research. Rethinking the design of Hypermedia systems from the developer’s perspective can both help the the web development community and the growth of the OHSs’ usage.

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Thank you!

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