Hermannus Balsters

An Object-Oriented Framework for Managing Cooperating Legacy Databases

We describe a general semantic framework for precise specification of so-called database federations. A database federation provides for tight coupling of a collection of heterogeneous legacy databases into a global integrated system. Our approach to database federation is based on the UML/OCL data model, and aims at the integration of the underlying database schemas of the component legacy systems to a separate, newly defined integrated database schema. Our approach to coupling of component databases into a global, integrated system is based on mediation. Our major result is that mediation in combination with a so-called integration isomorphism integrates component schemas without loss of constraint information; i.e., constraint information available at the component level remains intact after integration on the level of the virtual federated database. Our approach to integration also allows for specification of additional inter-database constraints between the component databases.

Semantics of information systems outsourcing

Businesses are in nature dynamic and change continuously. Because of different economic prospects they grow in size and portfolio or just the other way they have to reduce one of these aspects. There are several ways to accomplish growth or reduction. A smooth way may consist of outsourcing parts of one’s non-core business processes to specialized parties in the market. A variety of outsourcing models have been developed ([6]). Outsourcing can range from having all the business process (such as development, maintenance and operations) performed by an outsourcing partner, up to having a contract with a partner performing only one single business task. In our work we concentrate on conceptual modeling of outsourcing information systems, where outsourcing in the context of information systems will be defined as delegating a part of the functionality of the original system to an existing outside party (the supplier). Such functionality typically involves one or more operations (or services), where each operation satisfies certain input- and output requirements. These requirements will be defined in terms of the ruling service level agreements (SLAs). We provide a formal means to ensure that the outsourcing relationship between outsourcing party and supplier, determined by a SLA, satisfies specific correctness criteria. These correctness criteria are defined in terms of consistency and completeness between the outsourced operation and the associated operation offered by the supplier. Our correctness criterion will concern mappings between an existing outsourcer schema and an existing supplier schema, and will address both semantical and ontological aspects pertaining to outsourcing. Formal specifications as offered in our work can prove their value in the setup and evaluation of outsourcing contracts. We will perform our analysis within the modeling framework based on the UML/OCL formalism ([8,9]). The Object Constraint Language OCL offers a textual means to enhance UML diagrams, offering formal precision in combination with high expressiveness. In [1] it has been demonstrated that OCL has at least the same expressive power as the relational algebra, (the theoretical core of the relational query language SQL), thus making OCL a very powerful language for specification of constraints, queries and views.