1. 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
HT04: International Workshop on Web Engineering

2. Introduction Popularity of the Web
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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HT04: International Workshop on Web Engineering

3. Introduction
Web engineers have already paid great attention to the web application development procedure.
BUT
The Open Hypermedia Community has not yet:
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
Moreover, OHSs have not reached a satisfactory level of publicity and the Hypermedia service discovery issue still remains unaddressed
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HT04: International Workshop on Web Engineering

4. Introduction
This paper proposes a framework for enabling web developers to use hypermedia services into their applications.
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.
A, B, C Levels of Work: Focus on C Level.
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HT04: International Workshop on Web Engineering

5. Service Oriented Web Development
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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HT04: International Workshop on Web Engineering

6. Service Oriented Web Development
From the developer’s perspective: When a developer intends to use foreign services to his application, he:
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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HT04: International Workshop on Web Engineering

7. Developers’ requirements
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.
Briefly,
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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HT04: International Workshop on Web Engineering

8. 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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HT04: International Workshop on Web Engineering

9. Why hypermedia systems are not used efficiently in the web development?
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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HT04: International Workshop on Web Engineering

10. 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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HT04: International Workshop on Web Engineering

11. Service Discovery: Related Work
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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HT04: International Workshop on Web Engineering

12. Service Discovery: Architecture
Centralized Service Discovery
(e.g. UDDI)
Drawbacks
Fully dependent on one server
QoS
Distributed Service Discovery
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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HT04: International Workshop on Web Engineering

13. Service Discovery: Architecture
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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HT04: International Workshop on Web Engineering

14. 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 ad-hoc language
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HT04: International Workshop on Web Engineering

15. Introspection Capabilities of OHSs
HSDL should be structured in a standard way and should include the following information:
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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HT04: International Workshop on Web Engineering

16. Hypermedia Service Registry
Registry Fields
Owner Information
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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HT04: International Workshop on Web Engineering

17. 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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HT04: International Workshop on Web Engineering

18. 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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HT04: International Workshop on Web Engineering

19. Discovering Hypermedia services: a step-by-step example
H S
Directory
Interface
1. Requesting
HS Directory
Hypermedia Server
2. HSQL
3. Results in XML
Registration
6. Establishing Service Communication
Hypermedia Service Discovery Mechanism
5. Selecting (Getting HSDL File)
4. Resulting Services
Web Developer
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HT04: International Workshop on Web Engineering

20. 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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HT04: International Workshop on Web Engineering

21. Additional Tools Communication Protocol Awareness Therefore:
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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HT04: International Workshop on Web Engineering

22. 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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HT04: International Workshop on Web Engineering

23. 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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HT04: International Workshop on Web Engineering

24. Conclusions
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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HT04: International Workshop on Web Engineering

25. Thank you!
15/09/2019
HT04: International Workshop on Web Engineering