Malcolm Attard
Department of Computer Science and AI, University of Malta
1. Introduction
- Ubiquitous coming from the Latin word ubique, means existing or being everywhere, especially at the same time
- Web Services are loosely specified and coupled components distributed over the internet with the purpose of being accessed and used ubiquitously by suppliers, customers, business and trading partners
2. Transactions
- Transactions are essential factor for web services adoption
- Business Transaction Protocol (BTP) specification aims to solve these problems by extending conventional methods to enable both ACID and non-ACID transactions using a two phase commit model based on structures defined as ATOMS and Cohesions
- WS-Coordination
* An activation service
* A registration service
* A coordination service
- WS-Transaction
* atomic transactions protocols for short lived transactions
* business transactions protocols for long lived transactions
- Services are created and registered via WS-Coordination services and their execution coordinated by the WSTransaction protocols
3. Security
- SAML’s objective was to enable interoperability of security services across the internet, where security information is transmitted using XML
- SAML provides a way to encapsulate the authentication process and provide transport for it
- WS-Security extends the use of XML Encryption and XML Signature for protection and verification respectively
- SAML it does not specify authentication mechanisms but uses SOAP messages and describes how to attach signature and encryption headers to SOAP
4. Quality of Service
- major requirements for a quality web service
* Availability - service needs to be present and ready for use
* Integrity - maintain correctness of interaction
* Accessibility - be capable of serving a web service request
* Performance - have a certain level of throughput and latency
* Reliability - maintain the service itself and the service quality
* Regulatory - comply with standards and conform to the devised rules
* Security - provide the agreed level of security
* Transactional Qualities - conserve the stabilized transactional behavior
- WSDL does not specify semantics or aspects regarding the Quality of the Service
- QoS web based services at different levels including the network level, the system level, the web server level and the service level
- Negotiation of web services and their QoS properties usually involves the creation of Service Level Agreements (SLAs)
5. Semantics
- RDF is have data defined and linked in such a way to achieve better use of the information on the internet
- DAML-S is a proposed DAML+OIL ontology which has the purpose of describing the behavior, properties and capabilities of web services
6. Composition
- Web Services Composition involves the combination of a number of web services to produce a more complex and useful service
- Choreography is the term used to define the tracking of message exchange between services while the term orchestration is used to refer to the services interaction involving the logic and order of interaction execution
- BPEL4WS(Business Process Execution Language for Web Services)
7. UbiWSCo
- web service composition definitions and methodologies and the development of a method, accompanied by its implementation (Ubiquitous Web Services Composer), which will enable us to compose a new service, from a number of other web services, automatically
- Our approach will take into consideration pre-defined compositions, service usage history, the actual user needs, the services’ SLAs and also the usage context of the service
- We intend to use BPEL4WS together with the complementary specifications WS-Transactions and WS-Coordination based definitions for the purpose
8. Related Work
- WeSCoS (Web Service Composition Framework) was developed to provide a research framework for composition of loosely coupled services
- SWORD is another tool set for Web Services Composition which uses a rule-based expert system to determine whether a service can be composed using existing services
- SWORD is focused towards information providing services and it can generate a functional composition plan given the functional requirements
지금 ITRC Project로 하고 있는 Ubiquitous Web Services의 모태가 되고, 교수님의 project에 대한 개념인지 알고 이 논문을 접하게 되었는데 생각보다 유비쿼터스 측면에 초점을 맞추고 있지는 않다.
Web Service나 SOA의 측면에서 바라보고 BPEL이나 WS-I에 대한 설명을 갖추고 이 논문의 구현에 필요한 사항을 논하고 있다.
하지만, 개념적으로 여러가지 기술에 대한 연결을 이야기하고 있기 때문에 정리하기는 좋다. 무엇무엇을 생각해야 하는지 제시하고 있다. 한 번 읽어보는 것이 좋을 것이다.
[20080131]NIA 올해의 유비쿼터스 10대 키워드 이슈 선정.pdf