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                  Dept. of Computer Science                              1-2/93
            Announcements of new Technical Reports
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TITLE    = Aliasing and Groundness Analysis of Logic Programs through 
           Abstract Interpretation and its Safety
NUMBER	 = 92-27
AUTHORS	 = Werner Hans and Stephan Winkler
PAGES	 = 30
ABSTRACT = This paper describes a safe method, which derives aliasing and 
           groundness properties of logic programs (with equality). The abstract
           domain bases on the one proposed by Jacobs and Langen, which has the
           advantage of great potential precision and supports the simple 
           computation through abstract interpretation. The abstract execution 
           follows the framework suggested by Bruynooghe determining useful
           information for all points within the program. The abstract 
           operations as well as the embedding in this framework are formulated 
           in a precise manner and are proven correct; the latter is the crucial
           topic here. In addition, several refinements are examined.

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TITLE    = Object-Orientation Axiomatised by Dynamic Logic
NUMBER	 = 92-30
AUTHORS	 = A. Kemper, G. Moerkotte, K. Peithner
PAGES	 = 31
ABSTRACT = The field of object-oriented databases is suffering from the lack
           of a---widely agreed upon---formal model. In this paper we develop 
           the basics of a formal model for an object-oriented data model 
           (kernel). The formalization is based on dynamic logic: combining 
           many-sorted algebras with states and state transitions. The
           many-sorted algebras are utilized to model the static aspects, i.e., 
           the value-oriented part of the object model.  The state transitions
           account for the dynamic behavior of the object base due to object
           modifications. The main dynamic features that we incorporate in the
           formal model comprise (object) attribute assignment, object creation,
           object deletion, and set object manipulation, i.e., removing and 
           inserting elements.

           The virtues of the proposed model are demonstrated on three sample
           applications. Dangling references may lead a given program to
           non-terminate---we will show this fact. Second, a desirable property
           of a program will be verified. Last, the semantics of a simple 
           declarative language for our object model will be specified. 
           Utilizing the formal model we are able to prove the correctness 
           of a particular query evaluation plan---called the ``nested loop''
           evaluation. 

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TITLE	 = Implementation of the imperative / rule based language PROGRES
NUMBER	 = 92-38
AUTHORS	 = Albert Zuendorf
PAGES	 = 12
ABSTRACT = The work reported here is part of the PROGRES (PROgrammed Graph 
           Rewriting Systems) project. PROGRES is a very high level multi 
           paradigm language for the specification of complex structured data 
           types and their operations. The data structures are modelled as 
           directed, attributed, node and edge labelled graphs (diane graphs). 
           The basic programming constructs of PROGRES are graph rewriting rules
           (productions and tests) and derived relations on nodes (paths and
           restrictions). These basic operations may be combined to build partly
           imperative, partly rule based, complex graph transformations by 
           special control structures which regard the nondeterministic nature
           of graph rewriting rules. PROGRES offers its users a convenient,
           partly textual, partly graphical concrete syntax and a rich system of
           consistency checking rules for the underlying calculus of programmed 
           diane-graph rewriting systems.

           This paper presents the key techniques used for the execution of 
           PROGRES programs. We will discuss a simple approach to control flow
           backtracking which is done in a conventional imperative programming 
           language by using a certain programming style. Additionally, the 
           semantics of PROGRES demands that we are able to restore arbitrary
           previous graph states during backtracking. This adds a new quality to
           the problem of backtracking which is addressed using a nonstandard
           database management system and its undo / redo mechanism. We believe 
           that the techniques presented here are not specific for the language 
           PROGRES but are useful for the implementation of a whole new family 
           of multiple paradigm languages.

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TITLE    = Intelligentes Backtracking bei der Auswertung funktional-logischer
           Programme (written in german)
NUMBER   = 92-39 
AUTHORS  = Patrik Koch
PAGES    = 45
ABSTRACT = Deklarative Programmiersprachen erm"oglichen eine problemorientierte 
           Beschreibung von Sachverhalten. Andererseits verursacht diese gro"se 
           Distanz zur realen Maschine Effizienzprobleme bei der Auswertung
           solcher Programme. In dieser Arbeit wird ein Intelligentes 
           Backtracking - Verfahren f"ur die Auswertung von Programmen der 
           funktional-logischen Sprache Babel vorgestellt. Dabei wird der
           Suchraum zum Auswertungszeitpunkt aufgrund der bisherigen Berechnung 
           dynamisch verkleinert.

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TITLE    = Design and Evaluation of GRAS, a Graph-Oriented Database
           System for Engineering Applications
NUMBER   = 92-44
AUTHORS  = N. Kiesel, A. Schuerr, B. Westfechtel
PAGES    = 44
ABSTRACT = Modern software systems for application areas like CAD, office
           automation, or software engineering are usually highly interactive
           and deal with rather complex object structures. For the realization
           of these systems a nonstandard database system is needed which is
           able to efficiently handle different types of coarse- and fine-
           grained objects (like documents and paragraphs), hierarchical and
           nonhierarchical relationships between objects (like composition-
           links and cross-references), and finally attributes of rather
           different size (like chapter numbers and bitmaps). Furthermore,
           this database system should support computation of derived data,
           undo/redo of data modifications, error recovery from system
           crashes, and version control mechanisms. In this paper, we
           describe the underlying data model and the functionality of GRAS,
           a database system which has been designed according to the above
           mentioned requirements. Furthermore, we motivate our central
           design decisions concerning its realization, and we evaluate
           our system by means of the so-called hypermodel benchmark for
           hypertext databases.

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Guido Hogen
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