Giuliano Pacini

Automating visual language generation

A system to generate and interpret customized visual languages in given application areas is presented. The generation is highly automated. The user presents a set of sample visual sentences to the generator. The generator uses inference grammar techniques to produce a grammar that generalizes the initial set of sample sentences, and exploits general semantic information about the application area to determine the meaning of the visual sentences in the inferred language. The interpreter is modeled on an attribute grammar. A knowledge base, constructed during the generation of the system, is then consulted to construct the meaning of the visual sentence. The architecture of the system and its use in the application environment of visual text editing (inspired by the Heidelberg icon set) enhanced with file management features are reported. >

Symbol-Relation Grammars

A common approach to the formal description of pictorial and visual languages makes use of formal grammars and rewriting mechanisms. The present paper is concerned with the formalism of Symbol?Relation Grammars (SR grammars, for short). Each sentence in an SR language is composed of a set of symbol occurrences representing visual elementary objects, which are related through a set of binary relational items. The main feature of SR grammars is the uniform way they use context-free productions to rewrite symbol occurrences as well as relation items. The clearness and uniformity of the derivation process for SR grammars allow the extension of well-established techniques of syntactic and semantic analysis to the case of SR grammars. The paper provides an accurate analysis of the derivation mechanism and the expressive power of the SR formalism. This is necessary to fully exploit the capabilities of the model. The most meaningful features of SR grammars as well as their generative power are compared with those of well-known graph grammar families. In spite of their structural simplicity, variations of SR grammars have a generative power comparable with that of expressive classes of graph grammars, such as the edNCE and the N-edNCE classes.

Efficient parsing of multidimensional structures

Visual languages have motivated growing interests in the investigation of grammatical formalisms and parsing algorithms for modelling and recognizing multidimensional structures. The effectiveness of visual languages require that some efforts must be accomplished to obtain efficient parsing techniques. A general parsing scheme for relation grammars is presented. The class RG/1 of grammars is characterized which seems to be well suited for modelling visual languages of practical use. An efficient O(n log n) parsing algorithm is also given.<<ETX>>

Relation grammars for modelling multi-dimensional structures

Relation grammars (RGs) are introduced as a possible general framework for specifying the syntax of visual languages and, more generally, of multi-dimensional languages. A formal definition of relation grammars is given. Two examples of applications on graphs are shown. RG formalism is compared to conventional context-free grammars. RGs are used to describe the syntax of horizontal lines and statechart graphs using picture processing grammars and picture layout grammars, respectively.<<ETX>>

Two-level control structure for nondeterministic programming

The basic ideas of nondeterministic programming are critically reconsidered to single out a proper attitude and programming style for languages allowing direct control of nondeterministic features. The proposed attitude aims at retaining the purity of the nondeterministic formulation of search processes on one level (the attempt level), deferring the coordination of problem solving efforts to another (the choice level). The feasibility of recognizing these two levels is discussed, stressing that the structure to be managed at the choice level is a tree of contexts. The leaves are computational environments, each holding an alternative under inspection, while the other nodes are associated with choice points. According to the proposed programming style, a generative function is associated with each choice point, which expresses the desired choice strategy. The main advantage of this approach is the localization of the search strategies: Each nonterminal node of the tree keeps track of the state of the computation as it was when the choice point was last interrogated, holding at the same time the strategy to coordinate the available alternatives. Examples are given in term of ND-Lisp, an extension of Lisp designed and implemented according to these guidelines.

Graph Representation and Computation Rules for Typeless Recursive Languages

Computations are carried out in recursive languages by the iterative application of two kinds of transformation rules (substitution and simplification rules) to an initial term.

Querying of executable software specifications

The availability of executable specification languages allows testing to be carried out soon after or concurrently with the requirements specification phase. In addition, it becomes possible to use these languages for rapid prototyping, making it possible to gather information on properties of the specified target system including its behavior in response to external events. The inspection of software behavior is viewed as the querying of executable specifications. A language RSQ is defined for the purpose of constructing queries against executable specifications expressed in RSF, a language for the description of systems with time constraints. A query is able to single out a subclass of possible behaviors based on properties supplied by the query. The integration of RSQ with RSF enhances the analytical abilities of the software designer and developer. >

Information management in context trees

SummaryInformation management in context trees involves three principal problems: retrieval, updating and garbage collection. These problems are discussed in the paper, and solutions are proposed and motivated. A list organization and relative algorithms to implement context trees are presented. Finally, experimental results are reported about the behaviour of a system which exploits context trees.

Redundancy Elimination and Loop Checks for Logic Programs

A simple analysis of the arguments developed by Bol et al. (Theoret. Comput. Sci.86, 35-79 (1991)) shows that an actual reason for the nonexistence of a complete sound simple check for all function-free programs is the presence in the resolvents of potentially unlimited sequences of atoms chained by common variables. This hints that a limitation of the number of variables generating this kind of chain could guarantee the applicability of complete simple loop checks. This line is followed in the paper, and quite general classes of logic programs are characterized, without any direct imposition on the structures of the rules. This objective is accomplished by exploiting a variant of SLD-resolution, which is able to perform a systematic elimination of redundant atoms from resolvents. As a notable result, it turns out that the equality loop check is complete for our class of logic programs. This seems to suggest that the necessity of using subsumption loop checks instead of equality checks is essentially due to the presence of redundant atoms in resolvents.

Multimodal presentation of dynamic object scenarios on the web

We describe a Web based presentation system for dynamic object scenarios. The system produces multimodal presentations based on 3D interactive animations, coordinated with adaptive spoken comments. User profiling and comments production are performed through the interaction with a human-like agent. The system has been developed as part of a research project on support tools for learning about sail racing rules and strategies. The presentation system works in conjunction with an expert authoring system for sail racing scenarios. The software architecture is modular and flexible, explicitly targeted to the Web environment. Moreover it is general enough to be easily reused in other domains and applications involving dynamic object scenarios.