Karvounarakis, Grigoris

Email Address
ORCID
Disciplines
Research Projects
Organizational Units
Position
Introduction
Research Interests

Search Results

Now showing 1 - 2 of 2
  • Publication
    Beyond Discrete E-Services: Composing Session-oriented Services in Telecommunications
    (2001-09-14) Christophides, Vassilis; Hull, Richard; Karvounarakis, Grigoris; Kumar, Akhil; Tong, Geliang; Xiong, Ming
    We distinguish between two broad categories of e-services: discrete services (e.g., add item to shopping cart, charge a credit card), and session-oriented ones (teleconference, collaborative text chat, streaming video, c-commerce interactions). Discrete services typically have short duration, and cannot respond to external asynchronous events. Session-oriented services have longer duration (perhaps hours), and typically can respond to asynchronous events (e.g., the ability to add a new participant to a teleconference). When composing discrete e-services it usually suffices to use a process model and engine that composes the e-services as relatively independent tasks. But when composing session-oriented e-services, the engine must be able to receive asynchronous events and determine how and whether to impact the active sessions. For example, if a teleconference participant loses his wireless connection then it might be appropriate to trigger an announcement to some or all of the other participants. In this paper we propose a process model and architecture for flexible composition and execution of discrete and session-oriented services. Unlike previous approaches, our model permits the specification of scripted "active flowcharts" that can be triggered by asynchronous events, and can appropriately impact active sessions. We introduce here a model and language for specifying process schemas (essentially a collection of active flowcharts) that combine multiple e-services, and describe a prototype engine for executing these process schemas.
  • Publication
    Optimizing Taxonomic Semantic Web Queries using Labeling Schemes
    (2004-01-01) Christophides, Vassilis; Karvounarakis, Grigoris; Plexousakis, Dimitris; Vouton, Vassilika; Scholl, Michel; Tourtounis, Sotiris
    This paper focuses on the optimization of the navigation through voluminous subsumption hierarchies of topics employed by Portal Catalogs like Netscape Open Directory (ODP). We advocate for the use of labeling schemes for modeling these hierarchies in order to efficiently answer queries such as subsumption check, descendants, ancestors or nearest common ancestor, which usually require costly transitive closure computations. We first give a qualitative comparison of three main families of schemes, namely bit vector, prefix and interval based schemes. We then show that two labeling schemes are good candidates for an efficient implementation of label querying using standard relational DBMS, namely the Dewey Prefix scheme and an Interval scheme by Agrawal, Borgida and Jagadish. We compare their storage and query evaluation performance for the 16 ODP hierarchies using the PostgreSQL engine.