Reasoning with graph constraints

Graph constraints were introduced in the area of graph transformation, in connection with the notion of (negative) application conditions, as a form to limit the applicability of transformation rules. However, we believe that graph constraints may also play a significant role in the area of visual software modelling or in the specification and verification of semi-structured documents or websites (i.e. HTML or XML sets of documents). In this sense, after some discussion on these application areas, we concentrate on the problem of how to prove the consistency of specifications based on this kind of constraints. In particular, we present proof rules for two classes of graph constraints and show that our proof rules are sound and (refutationally) complete for each class. In addition, we study clause subsumption in this context as a form to speed up refutation.     

Monomers of human beta 1 beta 1 alcohol dehydrogenase exhibit activity that differs from the dimer

A previously unreported enzymatic activity is described for monomers of the beta 1 beta 1 isoenzyme of human alcohol dehydrogenase that were prepared from dimeric enzyme by freeze-thaw in liquid nitrogen. Whereas the dimeric enzyme has optimal activity at low substrate concentrations (2.5 mM ethanol, 50 microM NAD+; "low Km" activity), the monomer has its highest activity at high substrate concentrations (1.5 M ethanol, 2.5 mM NAD+; "high Km" activity). While the activity of the monomer does not appear to be saturated at 1.5 M ethanol, its maximal activity at this high ethanol concentration exceeds the Vmax of the dimer by about 3-fold. The apparent Km of NAD+ with monomers is 270 microM, and no activity could be detected with nicotinamide mononucleotide as cofactor. During gel filtration the high Km activity elutes at a lower apparent molecular weight position than the dimer. The kinetics of monomer-to-dimer reassociation are consistent with a second-order process with a rate constant of 240 M-1 s-1. The reassociation rate is markedly enhanced by the presence of NAD+. During refolding of beta 1 beta 1 following denaturation in 6 M guanidine hydrochloride, an enzyme species with high Km activity and spectral properties similar to the freeze-thaw monomer is observed, indicating that a catalytically active monomer is an intermediate in the refolding pathway. The enzymatic activity of the monomer implies that the intersubunit contacts of beta 1 beta 1 are not crucial in establishing a catalytically competent enzyme. However, the differences in specific activity and Km between monomer and dimer suggest that dimerization may serve to modulate the catalytic properties.     

Canonical constraints for parameterized data types

This paper presents a comparatively general method for specifying a ‘data constraint’ on a parameterized data type (i.e., specifying just which category of algebras it is supposed to be defined or correct on), and shows that there is a simple canonical form for such constraint specifications. We also show how such constraints may be employed to give ‘loose’ specifications of data types.     

Object-Oriented Connector-Component Architectures

This paper presents an important extension of our contribution to FESCA '04, which presented a generic framework for connector architectures. These architectures were defined by components, consisting of a body specification and a set of export interfaces, and connectors, consisting of a body specification and a set of import interfaces plus connecting transformations in both cases. A major restriction of this framework was given by the assumption of non-overlapping connector interfaces.In order to make the generic framework for connector architectures more applicable, it is enriched by the possibility of handling overlapping connector interfaces. Fortunately, it is possible to extend the main results presented at FESCA '04 also to the new framework. Moreover, it is shown that the new framework can be applied to UML class diagrams, state machines and sequence diagrams as heterogeneous specification techniques. The resulting connector framework, including a concept for the composition of components and architectural reduction for UML specifications, is illustrated by a case study concerning the meta data management in Topic Maps.     

Applications of graph grammar theory to consistency,synchronization and scheduling in data base systems

Graph grammar concepts are applied for the design of consistent states and manipulations modeling actions, transactions and schedules for simultaneous executions on data base systems. Especially we show how to use Church-Rosser Theorems for graph grammars to handle synchronization problems for data base systems in a multi-user environment. In this paper theses concepts are applied to a data base system for a library. For reasons of presentation the system is restricted to the basic features of a library but can be extended to more comfortable systems including also generalized data base systems. All manipulation rules are shown to preserve consistency and it is analysed exactly which of theses rules are collateral and for which of them further synchronization mechanisms are necessary. While consistent states are modelled as graphs and manipulation rules (resp. actions) as graph productions transactions correspond to sequences of productions, and schedules to sequences of parallel productions. The application of a schedule to a consistent state yields a “semantical schedule” which transforms the given state to some other state of the system. Sufficient conditions are given for a schedule to be consistent which means that consistent states are transformed into consistent states. Moreover we are able to define a degree of non-parallelism for schedules such that optimal schedules are those with minimal degree with respect to all equivalent ones. Applying results from graph grammar theory we are able to show that for each schedule there is a unique optimal one. A similar result is shown for semantical schedules where the semantical degree of non-parallelism is smaller than the syntactical one in general.     

Algebraic implementation of abstract data types

Starting with a review of the theory of algebraic specifications in the sense of the ADJ-group a new theory for algebraic implementations of abstract data types is presented.While main concepts of this new theory were given already at several conferences this paper provides the full theory of algebraic implementations developed in Berlin except of complexity considerations which are given in a separate paper. The new concept of algebraic implementations includes implementations for algorithms in specific programming languages and on the other hand it meets also the requirements for stepwise refinement of structured programs and software systems as introduced by Dijkstra and Wirth. On the syntactical level an algebraic implementation corresponds to a system of recursive programs while the semantical level is defined by algebaic constructions, called synthesis, restriction and identification. Moreover the concept allows composition of implementations and a rigorous study of correctness. The main results of the paper are different kinds of correctness criteria which are applied to a number of illustrating examples including the implementation of sets by hash-tables. Algebraic implementations of larger systems like a histogram or a parts system are given in separate case studies which, however, are not included in this paper.     

Transformations of structures: An algebraic approach

This paper introduces a new mathematical approach to transformations of structures, where the concept of structure is extremely general. Many structures and transformations that arise in biology as well as computer science are special cases of our concepts. A structure may be changed by finding an occurrence of a pattern and replacing it by another pattern as specified by a rule. To prove theorems about long sequences of applications of complicated rules, we need precise and tractable mathematical definitions of rules and how to apply them. This paper presents such definitions and three fundamental theorems, together with brief remarks on applications to control flow analysis, record handling, and evaluation of recursively defined functions. Unlike some previous efforts toward a rigorous theory of transformations of structures, this paper uses ideas and results from abstract algebra to minimize the need for elaborate constructions.A condensation of an earlier version of this paper was presented as [9] at the 7th Symposium on Mathematical Foundations of Computer Science, September 1978, Zakopane, Poland. Work by Ehrig was partially supported by IBM Germany and IBM World Trade Corp. Work by Rosen and Maggiolo-Schettini was partially supported by the Laboratorio di Cibernetica del C.N.R.     

Muskuloskeletale Belastungen im Schafshinterlauf: Mechanische Rahmenbedingungen der Heilung

Musculoskeletal loading in the sheep hind limb: Mechanical boundary conditions for healing Although the sheep is a standard model for the analysis of biological healing processes after surgical intervention at the knee and shank, the in vivo tibio‐femoral joint contact forces and the resulting musculoskeletal loading conditions have yet to be studied in detail. The three‐dimensional kinematics of three Merino‐mix sheep right hind limbs were recorded using reflective markers that were attached to Schanz’ screws, firmly anchored in the bone. This motion data was used together with the simultaneously measured external loading (ground reaction forces) to calculate the muscle and joint contact forces, as well as the internal loads within the bones. Whilst the motion mainly occurred in the sagittal plane, significant out of plane motion was observed, especially at the hip and knee joint (ab/adduction hip: 13°, knee: 10°; internal/external rotation hip: 12°, knee: 14°). The axial component of the tibio‐femoral contact force was 2.1 times body weight (BW). The medio‐lateral and anterior‐posterior shear forces amounted to only 0.7 times BW. The loading in the diaphysis of the tibia under physiological musculoskeletal conditions was mainly axial compression (0.89 BW) together with only small shear forces (0.15 BW). The results of the musculoskeletal analyses presented here add to the understanding of the mechanical loading conditions in sheep. This expanded knowledge aids in the interpretation of studies of the sheep tibia and their relevance for the clinical situation of the human patient.