Modeling Of Complex Objects Research Articles

A rule-based update language for complex objects with identity

This paper deals with the definition of a rule-based update language for complex object databases. Several update operators are introduced, which correspond to basic manipulations of data entities with object identity. These operators can be used in rule bodies for specifying complex update transactions. The syntax and the semantics of the language is given in the framework of CO, a simple data model for complex objects with identity. An interpreter of the language is defined and its correctness is discussed. Finally, the issue of maintaining database consistency with respect to several kinds of integrity constraints is illustrated.

Index configuration in object-oriented databases

In relational databases, an attribute of a relation can have only a single primitive value, making it cumbersome to model complex objects. The object-oriented paradigm removes this difficulty by introducing the notion of nested objects, which allows the value of an object attribute to be another object or a set of other objects. This means that a class consists of a set of attributes, and the values of the attributes are objects that belong to other classes; that is, the definition of a class forms a hierarchy of classes. All attributes of the nested classes are nested attributes of the root of the hierarchy. A branch of such hierarchy is called a path. In this article, we address the problem of index configuration for a given path. We first summarize some basic concepts, and introduce the concept of index configuration for a path. Then we present cost formulas to evaluate the costs of the various configurations. Finally, we present the algorithm that determines the optimal configuration, and show its correctness.

Modeling with triangular B-splines

Triangular B-splines are a new tool for modeling complex objects with nonrectangular topology. The scheme is based on blending functions and control points, and lets us model piecewise polynomial surfaces of degree n that are C/sup n-1/-continuous throughout. Triangular B-splines permit the construction of smooth surfaces with the lowest degree possible. Because they can represent any piecewise polynomial surface, they provide a unified data format. The new B-spline scheme for modeling complex irregular objects over arbitrary triangulations has many desirable features. Applications like filling polygonal holes or constructing smooth blends demonstrate its potential for dealing with concrete design problems. The method permits real-time editing and rendering. Currently, we are improving the editor to accept simpler user input, optimizing intersection computations and developing new applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Exploring communication in collaborative design: co-operative architectural modelling

An exploration of communication in collaborative design from the perspective of co-operative architectural modelling is reported. The objectives and problems of communication in collaborative design are described and anaysed by viewing design as, basically, disciplines of modelling complex objects. Three cases of teamwork in architectural modelling are studied, each demonstrating a rich and informative approach to collaboration. Looking at the cases from the co-operative modelling perspective, important conditions for communication are observed: firstly, the participation and co-ordination among heterogeneous systems of representation and action that individual members of a design team work with; and secondly, the interconnection between common goals shared by all participants and domain-oriented goals pursued by individuals. In exploring how the conditions were met, it was found useful to characterize communication in terms of the inter-relations between common images and distributed design developments. Two generic patterns of communication in collaborative design were found, which suggest two alternative conceptual frameworks for developing computational representations.

Implementation of a graph-based data model for complex objects

We have developed a graph-based data model called the Hypernode Model whose single data structure is the hypernode , a directed graph whose nodes may themselves reference further directed graphs. A prototype database system supporting this model is being developed at London University as part of a project whose aims are threefold: (i) to ascertain the expressiveness and flexibility of the hypernode model, (ii) to experiment with various querying paradigms for this model, and (iii) to investigate the suitability of the directed graph as a data structure supported throughout all levels of the implementation. The purpose of this paper is to report upon our findings to date.

A Fully Precise Null Extended Nested Relational Algebra

The nested relational model extends the fiat relational model by relaxing the first normal form assumption in order to allow the modelling of complex objects. Recently many extended algebras have been suggested for the nested relational model, but only few have incorporated null values into the attribute domains. Furthermore, some of the previously defined extended algebras are defined only over a subclass of nested relations, and all of them are difficult to use, since the user must know the detailed structure of the nested relations being queried. Herein, we define an extended algebra for nested relations, which may contain null values, called the null extended algebra. The null extended algebra is defined over the general class of nested relations with null values and, in addition, allows queries to be formulated without the user having to know the detailed structure of the nested relations being queried. In this sense, our null extended join operator of the null extended algebra is unique in the literature, since it joins two nested relations by taking into account all their common attributes at all levels of their structure, whilst operating directly on the two nested relations. All the operators of the null extended algebra are proved to be faithful and precise. The null extended algebra is a complete extended algebra in the context of nested relations, and, in addition, it includes the null extended powerset operator, which provides recursion and iteration facilities.

Semantics for null extended nested relations

The nested relational model extends the flat relational model by relaxing the first normal form assumption in order to allow the modeling of complex objects. Much of the previous work on the nested relational model has concentrated on defining the data structures and query language for the model. The work done on integrity constraints in nested relations has mainly focused on characterizing subclasses of nested relations and defining normal forms for nested relations with certain desirable properties. In this paper we define the semantics of nested relations, which may contain null values, in terms of integrity constraints, called null extended data dependencies , which extend functional dependencies and join dependencies encountered in flat relational database theory. We formalize incomplete information in nested relations by allowing only one unmarked generic null value , whose semantics we do not further specify. The motivation for the choice of a generic null is our desire to investigate only fundamental semantics which are common to all unmarked null types. This lead us to define a preorder on nested relations, which allows us to measure the relative information content of nested relations. We also define a procedure, called the extended chase procedure , for testing satisfaction of null extended data dependencies and for making inferences by using these null extended data dependencies. The extended chase procedure is shown to generalize the classical chase procedure, which is of major importance in flat relational database theory. As a consequence of our approach we are able to capture the novel notion of losslessness in nested relations, called herein null extended lossless decomposition . Finally, we show that the semantics of nested relations are a natural extension of the semantics of flat relations.

Joining distributed complex objects: Definition and performance

The performance of a non-standard distributed database system is strongly ifluenced by complex objects. The effective exploitation of parallelism in querying them and a suitable structure to store them are required in order to obtain acceptable response times in these database environments where performance tends to be critical. In this paper we use an hierarchical complex object model with object references and define several join operations for these complex objects which we will call tuple objects. These join queries for tuple-objects can be categorized into materialized, functional and value-based joins. An analytical performance evaluation gives insight into which distributed storage structures for tuple-objects are most effective with regard to executing the different kinds of tuple-object joins.

ECLAIR: an Extensible Class Library for Information Retrieval

This paper describes ECLAIR, an extensible object-oriented class library, which can be used to construct information retrieval systems and applications. ECLAIR is implemented in C++ and uses an object-oriented database management system for persistent object storage. The library provides data structures and operations necessary to allow the efficient indexing, storage and retrieval of data items based on their text content using automatic indexing and best-match retrieval techniques. By exploiting the object-oriented paradigm, we have been able to develop a library which is usable by any application requiring information retrieval functionality, and further, is extensible such that many of the functions provided by the library can be changed as required by an application. Additionally, applications can exploit the features of the underlying object-oriented database management system, which include support for persistence of data (objects), modelling complex objects, concurrent access to data, and reliable processing of data in the presence of system failures. In the paper we consider how to deliver information retrieval functionality to the developers of application systems and we evaluate current approaches. The design and implementation of ECLAIR is described in detail. A number of experiments applying ECLAIR are reported.

A frame-based model for large manufacturing databases

A major requirement of database systems in engineering design and manufacturing applications is support for storage and maintenance of complex objects. Frame based systems are capable of modeling complex objects. However, many of these systems are implemented in main memory. As the number of objects to be stored far exceeds the capacity of the main memory of a computer, such an implementation is often unusable. Therefore, new ways to model and manipulate large manufacturing databases are needed. In this paper we present an implementation of a frame based system on top of the POSTGRES extensible database system. Such an implementation combines the advantages of database management and frame based systems and allows for the development of large manufacturing database applications with minimal effort.

A recursive algebra for nested relations

The nested relational model provides a better representational model for complex objects than the (flat) relational model by allowing relations to have relation-valued attributes. A recursive algebra for nested relations that allows relations to be accessed and modified at all levels without always having to flatten them is presented in this paper. The operators of the classical nested relational algebra are extended with recursive definitions so that they can be applied not only to relations but also to subrelations of a relation. Queries are much more efficient and succinct when expressed in this algebra than in languages that require restructuring in order to access subrelations of relations. A sketch of a proof showing the equivalence of the expressive powers of the recursive algebra and the nested relational algebra is given.

Complex-Prolog: A logic database language for handling complex objects

The logic language paradigm represents a natural extension of relational databases. However, one of its limitations is the lack of suitable data abstraction mechanisms for modeling complex objects. This paper describes Complex-Prolog, a logic database language that provides facilities for data abstraction, notably, the notions of object identity, class and inheritance. This language was designed as an attempt to integrate concepts from logic programming and semantic data models. A formal definition of Complex-Prolog, interspersed with a number of examples, is given. The paper concludes with a description of its implementation.

Hyperquadrics: Smoothly deformable shapes with convex polyhedral bounds

We present a new approach to the problem of modeling smoothly deformable shapes with convex polyhedral bounds. Our hyperquadric modeling primitives, which include superquadrics as a special case, can be viewed as hyperplanar slices of deformed hyperspheres. As the original hypersphere is deformed to its bounding hypercube, the slices undergo corresponding smooth deformations to convex polytopes. The possible shape classes include arbitrary convex polygons and polyhedra, as well as taperings and distortions that are not naturally included within the conventional superquadric framework. By generalizing Blinn's “blobby” approach to modeling complex objects, we construct single equations for nonconvex, composite shapes starting with our basic convex primitives. Hyperquadrics are of potential interest for the generation of synthetic images, for automated image interpretation and for psychological models of geometric shape representation, manipulation, and perception.

Extending the object-oriented paradigm for supporting complex objects

In this paper a generalized object-oriented approach for complex object modeling in proponed, which is characterized by adding the concept of Meta-Class into the object-oriented paradigm for unifying the handling of object types and primary data models, and also characterized by integrating the modeling of object type hierachy and object configuration hierarchy. Concepts such as Compositional Relationship Object, Face, Object Configuration Schema Expression, Object Skeleton are introduced to specify object structure, to support high degree of object sharing and to offer high degree of data independence. Operations on the class hierarchy, the object configuration structures and the object instances are developed respectively with distinguished semantics. This approach provides an extended object-oriented framework for handling complex objects in any AI or database systems.

Construction of fractal objects with iterated function systems

In computer graphics, geometric modeling of complex objects is a difficult process. An important class of complex objects arise from natural phenomena: trees, plants, clouds, mountains, etc. Researchers are at present investigating a variety of techniques for extending modeling capabilities to include these as well as other classes. One mathematical concept that appears to have significant potential for this is fractals. Much interest currently exists in the general scientific community in using fractals as a model of complex natural phenomena. However, only a few methods for generating fractal sets are known. We have been involved in the development of a new approach to computing fractals. Any set of linear maps (affine transformations) and an associated set of probabilities determines an Iterated Function System (IFS). Each IFS has a unique "attractor" which is typically a fractal set (object). Specification of only a few maps can produce very complicated objects. Design of fractal objects is made relatively simple and intuitive by the discovery of an important mathematical property relating the fractal sets to the IFS. The method also provides the possibility of solving the inverse problem. given the geometry of an object, determine an IFS that will (approximately) generate that geometry. This paper presents the application of the theory of IFS to geometric modeling.

Numerical calculations of low‐frequency TE fields in arbitrarily shaped inhomogeneous lossy dielectric cylinders

The Galerkin method with subsectional linear basis and weighting functions is used to calculate the low‐frequency transverse electric fields in lossy dielectric cylinders. Arbitrarily shaped polygonal cells are employed to allow more accurate modeling of complex objects without excessive matrix sizes. To demonstrate the validity of the method, the analytical and numerical solutions are compared for triple‐layered concentric cylinders. The calculated fields in a model of the human torso exposed to a solenoidal field are also presented. Among other applications, the method should be useful for evaluating electromagnetic (em) biohazards, and for analyzing and designing dielectric antennas and hyperthermia applicators at low frequencies.

Interactive graphics for volume modeling

This paper describes the GRaphic INput subsystem (GRIN) of an experimental volume modeling system called the Geometric Design Processor (GDP) developed at the IBM Thomas J. Watson Research Center. Sitting at an interactive graphic workstation, a mechanical designer generates computer volume models of complex physical objects and mechanisms built up from primitive volumes, e.g., cuboids, cylinders, swept surfaces, etc., entered at any orientation in 3-dimensional space. Objects are represented in the model as polyhedral approximations. The central issue is the provision of an efficient, natural means for a mechnical designer to enter and interact with these models.

GRIN: Interactive Graphics for Modeling Solids

This paper describes an experimental system for the original generation and subsequent modification of volume models of complex physical objects, using interactive computer graphics. The models are built up from primitive volumes, e.g., cuboids, cylinders, swept sutfaces, etc., entered by a mechanical engineer interacting with a two dimensional projection of the model on a graphic display screen. The primitives may be entered at any orientation in 3-space and combined to form a single polyhedral model. The central issue is the provision of an efficient, natural means for generating these models.