Today it is immediately visible that the future of distributed systems is aligned with the general idea of pervasive and ubiquitous computing, which consists of the gradual disappearance of stationary workstations and the distribution of information and computational power in the environment where the users of those systems live and work. Typical applications are met in places like airports, railway stations and shopping centers.

Assume an example from the area of vehicular technology. Several kinds of vehicles are driving on the highway from Marseilles to Barcelona. Each vehicle comprises web services, providing dynamically changing information regarding the vehicle’s location, velocity and fuel deposit. Moreover, each vehicle comprises services that offer static information concerning its type and technical characteristics. On the highway, there exist exits to parking areas, which may include facilities such as gas stations, fast food restaurants, medical help, and shopping centers. Each one of these facilities comprise web services, which range from simple ones, reporting the existence of the facility, to more complex ones providing information regarding for instance the price lists, the availability of certain goods or the number of patients waiting for medical help. The drivers of the vehicles may use/query several of the services provided during the drive. For instance, they may be interested in obtaining the following information: (a) The closest gas-station with a price of gasoline under 2 €/gallon. (b) The closest Italian restaurant. (c) Notification for the average speed of all the cars ahead.

The goal of this project, DIACHEO, is to define a framework for the support of database queries to ad hoc communities of mobile peers. The proposed infrastructure is based on standard database technologies for the top-level querying, ad-hoc mobile network technologies for the communications part and web services as a standard API via which the mobile peers exchange data.

 

The cornerstone of the proposed infrastructure is the fact that we replace the traditional treatment of databases as persistent collections of records by the assumption that a database relation is a collection of records dynamically compiled from such ad-hoc sets of peers. Each peer in such an environment has a database over which users want to execute queries. This database involves (a) relations which are locally stored and (b) relations which are virtual or hybrid. In the case of virtual relations, all the tuples of the relation are collected from peers that are present in the network at the time when the query is posed. Hybrid relations involve both locally stored tuples and tuples collected from the network. The collaboration among peers is performed through web services. The integration of the external data, before they are locally collected to a peer's database is performed through a workflow of web service invocations. Summarizing the problem, due to the transitive nature of the extent of virtual relations, we cannot perform query processing in the traditional way, but rather, we have to involve context-aware query processing techniques that exploit the neighborhood of each peer and the web service infrastructure that deals with the heterogeneity of peers. The approach of DIACHEO is based on a formal system model. Moreover, SQL^P, an extension of traditional SQL has been defined, on the basis of environment requirements that concern the termination of queries, the failure of individual peers and the semantic characteristics of the peers of the network. Initial results on the query execution as well as the typical definition of all the operators which can take place in a query execution plan have also been defined. [...Read more...]

Each peer offers data to the relations through a workflow of web services. Assume a peer u that poses a query and invokes web service operations from a set of peers u_1, u_2,….., u_z in order to collect their tuples. In principle, it is quite possible that the requested information from a certain peer can only be obtained after the invocation of a workflow of web service operations (rather than a single operation). For example, assume that a peer using the European metric system collects the velocities of other peers of class CAR, and a certain class of cars returns miles instead of kilometers. The conversion can be performed through a simple BPEL workflow. At the end of the execution of the workflow, the data are mapped to the target relation of the querying peer.

To efficiently support query management, it is necessary that the routing layer must cooperate effectively with the application layer in order for such an application to be developed. In the context of DIACHEO we have come up with a new routing and transport mechanism for wireless ad-hoc networks that incorporates application layer specifics in order to support both traditional and data-centric communications and at the same time optimizes the management of scarce network resources. Between the cross-layer technique and the exhaustive method of flooding, an intermediate mechanism has also been investigated, that deals with the problem of useless transmissions caused by the traditional method of flooding, thus considerably improving the routing of queries. The proposed cross-layer technique has been evaluated through extended simulations with certain parameters, executed in two types of wireless networks, namely ad hoc and mesh. [...Read more...]

1.

N. Folinas, P. Vassiliadis, E. Pitoura, E. Papapetrou, A. Zarras. Context-Aware Query Processing in Ad-Hoc Environments of Peers. Journal of Electronic Commerce in Organizations (JECO), 6(1), pp. 38-62, ISSN: 1552-6283, IGI Global.

2.

E. Papapetrou, E. Rova, A. Zarras, P. Vassiliadis. Cross-layer Networking for Peer Databases over Wireless Ad-Hoc Communities. In Proc. IEEE International Conference on Communications (ICC 2007), Glasgow, 24-28 June, 2007.

3.

K. Stamkopoulos, E. Pitoura, P. Vassiliadis, A. Zarras. Accelerating Web Service Workflow Execution via Intelligent Allocation of Services to Servers. Accepted at Journal of Database Management (JDM), ISSN: 1063-8016, IGI.

4.

K. Stamkopoulos, E. Pitoura, P. Vassiliadis. Efficient Deployment of Web Service Workflows. In Proc. 2nd International Workshop on Services Engineering (SEIW 2007), (in conjunction with ICDE 2007), Constantinople, Turkey, April 16, 2007.

5.

N. Polyzotis, S. Skiadopoulos, P. Vassiliadis, A. Simitsis, N.-E. Frantzell. Supporting Streaming Updates in an Active Data Warehouse. In Proc. 23rd International Conference on Data Engineering (ICDE 2007), pp 476-485, Constantinople, Turkey, April 16-20, 2007.

6.

A. Karakasidis, P. Vassiliadis, E. Pitoura. ETL Queues for Active Data Warehousing. In Proc. 2nd International Workshop on Information Quality in Information Systems (IQIS 2005), pp. 28-39, co-located with ACM SIGMOD/PODS 2005, June 17, 2005, Baltimore, MD, USA.

7.

E. Baikousi, P. Vassiliadis. Tuning the top-k view update process. 3rd Multidisciplinary Workshop on Advances in Preference Handling (M-Pref 2007), held in conjunction with VLDB 2007, Vienna, Austria, 23 September 2007.

 

Please contact the project's coordinator

 

Panos Vassiliadis

 

Distributed Management of Data Laboratory

 

Univ. of Ioannina, Dept of Computer Science

 

45110, Ioannina, Hellas

 

http://www.cs.uoi.gr/~pvassil

 

This research Project has been co-funded by the European Union - European Social Fund (ESF) & National Sources, in the framework of the program “Pythagoras II” of the “Operational Program for Education and Initial Vocational Training” of the 3rd Community Support Framework of the Hellenic Ministry of Education.