msiegelQsloan.mit.edu In this paper we describe a rule-based ap-proach to semantic specification that can be used to establish semantic agreement be-tween a source and receiver. Query process-ing techniques use these specifications along with conversion routines and query modifi-cation to guarantee correct data semantics. This work also examines the effect of chang-ing data semantics. These changes may oc-cur at the source of the data or they may be changes in the specifications of the dat,a semantics for the application, Methods are described for detecting these changes and for determining if the database can continue to supply meaningful data to the application. These methods for semanlic reconcilia2ion are necessary for determining logical connec-tivity between a data source (database) and a data receiver (application). Though de-scribed in terms of the source-receiver model, these techniques can also be used for seman-tic reconciliation and schema integration for multidatabase systems. Keywords[data dictionaries, heterogeneous databases, metadata, query modification, schema integration, seman-tic conflicts] 1

Reorganization of classes for object-oriented programming and object-oriented database design has recently received considerable attention in the literature. In this paper a small set of primitive transformations is presented which forms an orthogonal basis for object-preserving class reorganizations. This set is proven to be correct, complete, and minimal. The primitive transformations help form a theoretical basis for class organization and are a powerful tool for reasoning about particular organizations.

The contributions of this paper are two-fold: First we introduce a novel, axiomatically defined, object-oriented data model, called the Demeter kernel model, and second we present abstraction and optimization algorithms and their relationships for designing classes from objects in the kernel model. We analyze several computational problems underlying the class design process which is divided into two phases: a learning phase and an optimization phase. This study focuses on approximation algorithms for the optimization phase and leads to a better understanding and a partial automation of the object-oriented design process. The algorithms and the theory presented in this paper have been implemented in the C++ Demeter System TM , a CASE tool for object-oriented design and programming. Keywords: Object-oriented programming and design, reverse engineering, formal software engineering techniques, class hierarchy optimization. Acknowledgements: Preliminary versions of this paper ...

We argue that explanation-based generalisation as recently proposed in the machine learning literature is essentially equivalent to partial evaluation, a well known technique in the functional and logic programming literature. We show this equivalence by analysing the definitions and underlying algorithms of both techniques, and by giving a Prolog program which can be interpreted as doing either explanation-based generalisation or partial evaluation. 1 Introduction An interesting development in the field of machine learning is the advent of a technique called explanation-based generalisation (EBG). This name was first coined in [Mitchell et al., 1986], but the technique can be traced back to [Mitchell, 1983], and earlier to [DeJong, 1981] and [Mitchell, 1982]. This technique tackles the problem of formulating general concepts on the basis of specific training examples. For some considerable time, the functional programmingcommunity, and more recently the logic programming community, ...

ii Class organizations (schemas) evolve over the life cycle of object-oriented systems for avariety of reasons. This issue has recently been a subject of increasing attention in the literature of both object-oriented languages and object-oriented database systems. One of the most common forms of evolution involves the extension of an existing system by addition of new classes of objects or the addition of attributes to the original objects. Sometimes class structures are reorganized even when the set of objects is unchanged. In this case the reorganization might represent an optimization of the system, or just a change in the users ' perspective. At the other extreme, a class reorganization might re ect not only the extension and reclassi cation of existing objects, but also structural changes (other than addition of attributes) in the original objects. This work provides a mathematical treatment of a calculus of class transformations. Three kinds of transformations that commonly occur in the evolution of class structures are considered: object-extending, object-preserving, and language-preserving. For each kind of transformation, methods for automating the maintenance of systems based on the evolving class structure are discussed. The language-preserving transformations are a special case of transformations that change the structure of existing objects. If an object schema is decorated with concrete syntax, it de nes not only a class structure, but also a language for describing the objects. When two schemas de ne the same language but di erent classes, the language may be used to guide the discovery of analogies between the classes. The resulting analogies may then be used to transport functionality between domains. iii Acknowledgments Iwould like to thank my advisor, Karl Lieberherr, for his generous support, guidance, and feedback. I would also like to thank my wife, Vickie, for her constant encouragement and understanding without which thiswork would not have been possible. iv

ion of common parts and distribution of common parts are extended to apply to syntax edges as well as attribute edges. The only additional complexity is that abstraction of common parts to a superclass is restricted so that the ordering of parts at each immediate subclass cannot be changed. If there is a set of classes that have more than one part in common, but the common parts are ordered differently in the individual classes, then it is not possible to abstract all of the common parts. The object-preserving transformations for class graphs are as follows: ffl Renumbering of parts. Any set of attribute and syntax edges in a class graph may be renumbered as long as the ordering of parts (including inherited parts) remains unchanged for each class. ffl Abstraction of common parts. If all of the immediate subclasses of class C have the same part, that part can be moved up the inheritance hierarchy so that each of the subclasses will inherit the part from C, rather than duplicating the...

In order to design and develop object-oriented programs, one must experience what is known as a "paradigm shift". This shift requires that one do not think in terms of the procedures that a software system must perform, but rather in terms of the entities or objects that participate in the system. As programmers experience a paradigm shift, so must existing software systems somehow be transformed into object-orientation if they are to benefit from object-oriented features.

The monitor is defined as a real-time system that interacts with the network through an interface. The interface is specified by a set of state variables to which sensors are attached. The Entity-Relationship model is used to represent the software and hardware objects in the network. The interface is modeled using the Entity-Relationship model and a computation model. The computation model consists of a set of sample path and performance evaluation operators. It operates on the state variables of the interface. A set of examples is provided -- the modeling of a multiplexer, a switching node and the quality of service parameters -- to describe the model for the environment and the interface of the monitor. 56 3.1. Introduction As described in Chapter 2, the network monitor is defined as a real-time system that interacts with its environment, i.e., the network, in an asynchronous way. This interaction takes place through an interface. In this chapter, the environment model of the mo...

The organization of the knowledge base for monitoring and the related principles for knowledge representation are presented. The knowledge base consists of configuration, sensor, dynamic and statistical databases. The configuration database represents the system architecture of the network. The sensor database is set up based on the sensor configuration in the network. The dynamic database represents the data space generated by the state and event variables in the network. The statistical database is derived from the dynamic database through statistical operators and represents the data space generated by the performance parameters. 91 4.1. Introduction The environment model in Chapter 3 gives us the description of a network and the interface between the network and the monitor. In this chapter we will show how to structure the information about the network objects in a knowledge database. We will also show how to organize the knowledge database according to various time levels. Ou...

In this chapter, we discuss the implementation of the models and methodologies discussed in Chapters 3-5 for monitoring of integrated networks. Specifically, the implementation of monitoring schemes for MAGNET II in a software environment is discussed. A simulator for MAGNET II has been built and the appropriate state variables specified for monitoring. The implementation of the Knowledge Base for network resource managers has been studied. The experience gained from the implementation of the Knowledge Base for monitoring is mentioned. The influence of the information and computation models for monitoring on the design of the network simulator is also discussed. A set of objects for statistical operators, such as histogram, auto-correlation, and cross-correlation, are also investigated. 182 6.1. Introduction An environment was designed to simulate MAGNET-II (as shown in Figure 2-1), such that the performance of the network and the users' service can be monitored and evaluated. The ...