Raymond K. Wong

A data model and semantics of objects with dynamic roles

Although the concept of roles is becoming a popular research issue in object oriented databases and has been proven to be useful for dynamic and evolving applications, it has only been described conceptually in most of the previous work. Moreover, the important issues such as the semantics of roles (e.g., message passing) are seldom discussed. Furthermore, none of the previous work has investigated the idea of role player qualification, which models the fact that not every object is qualified to play a particular role. We present a data model and the semantics of roles. We discuss each of the above issues and illustrate the ideas with examples. From these examples, we can easily see that the problems we discussed are fundamental and indeed exist in many complex applications.

Combined effects of food quantity and quality on Cd, Cr, and Zn assimilation to the green mussel, Perna viridis

We examined the assimilation of Cd, Cr, and Zn by the green mussel Perna viridis under complicated food conditions, including combinations of different compositions and concentrations of food (diatom and sediment), and variable food quantity and quality during particle digestion. At different combinations of food composition and quantity (5 mg l−1 and 20 mg−1, below and above the pseudofeces production), the Cd assimilation was significantly dependent on the food composition. The Cd assimilation efficiency (AE) decreased with increasing proportions of sediments in the diets, but its assimilation was not significantly affected by food concentration. In contrast, the assimilation of Cr and Zn decreased significantly with increasing food concentrations, whereas food composition did not significantly affect their AEs. Variations in metal gut passage time accounted partially for the difference in AEs among different combinations of food composition and quantity. By changing the type of particles during metal digestion, their AEs were maintained comparably at a low particle load (1 mg l−1), suggesting that variation of food quality during digestion did not affect metal assimilation. At a higher particle load (5 mg l−1), variation of food type during digestion affected the AEs of Cr and Zn. An increase in food concentrations from 1 to 15 mg l−1 during digestion resulted in a significant decrease in the AEs of Cr and Zn bound with either sediments or diatoms. Conversely, decreasing the food concentrations from 15 to 1 mg l−1 did not affect the AEs of metals, except for Zn bound with diatoms. Overall, our results highlighted the metal-specificity in their assimilation as influenced by complicated food environments, probably caused by different metal geochemical and biological behavior in the mussels. Feeding selectivity may have a greater control on the influx rate into the mussels than metal assimilation.

Dynamic knowledge representation in DOOR

In many class based, object oriented database systems the association between an instance and a class is both exclusive and permanent. Therefore, these systems have serious difficulties in representing objects taking on different and multiple roles over time, and hence cannot model the dynamic knowledge from the real world. The paper describes a novel object oriented database management system, called DOOR, which supports object evolution, dynamic role (context dependent) modeling, objects of multiple specific classes, and object role relationships. In DOOR, a role is an entity with state and behavior, but it does not have a globally unique identity. Therefore, its existence has to be associated with an object. A role acts as a special association between its owner and player, such that its owner can prescribe its state and its player gains its properties through dynamic role playing. In this way, an object can evolve dynamically and cooperatively according to its associated objects.

RBAC support in object-oriented role databases

‘I’hc research on object-oriented role databases has bccoiiif~ a,ctive recc>ntly. Parallel to this, the concept of roles have also been proposed in the context of access control and security management. It is interesting to irrvestigate whether the role concept proposed in these two di flerent contexts can be unified. This paper proposes the framework for ot)ject-orietlt,ed role database syst,ems which can be used as the basis for specifying and implementing rob-based access control (RHAC). The paper firstly surveys the state of the art in object-oriented role database concepts and models. To do this, we summarize our recently proposed object-oriented role database called DOOR., which includes most of the features of existing objt:ct-orierlted role systems. We then describe the authorization and security mechanisms of DOOR., and how to support RBAC with these mechanisms. In particular, we emphasize the RHAC issues to support authorization changes during object evolution.

Heterogeneous and Multifaceted Multimedia Objects in DOOR/MM

Although the distributed multimedia information system is getting popular nowadays, existing database systems do not offer adequate support to structural nor behavioral extension of multimedia objects. Moreover, the multifaceted nature of multimedia data has seldom been investigated. Besides the flexibility for multimedia authoring tools, dynamic extension and multifacet modeling can in general ease the task on integrating the multimedia information of heterogeneous formats over a distributed network. This paper presents the support of dynamic extension and multifacet modeling of multimedia objects in a client-server, object-role database system called DOOR. The resultant system, with multimedia functionalities, is named as DOOR/MM (DOOR with multimedia extensions). First, the underlying data model for DOOR is summarized. We then present the extension of the data model, by means of meta-object protocol (MOP), to implement the metaclasses for multimedia objects. In DOOR, objects are structured as a tree of roles. Each role may carry different properties and interact with other roles cooperatively. An object may acquire or drop multiple roles during its lifetime. Structural and behavioral extensions of multimedia objects are achieved by dynamic role playing. Multifaceted interfaces of an multimedia object are modeled by means of views on roles. In particular, we discuss different ways of using views to model different abstraction levels of the heterogeneous multimedia resources. Throughout the paper, examples such as text, bitmap, MIDI, and 3D graphic objects are used to demonstrate the significance of our approach.

An Efficient Indexing Scheme for Objects with Roles

Indexing schemes for traditional Object-Oriented Databases (OODBs) are divided into two catalogues: class hierarchy indexing and nested indexing. Since most of these systems are static in nature, dynamic operations like class versioning and role playing are not supported by traditional indexing schemes. In order to support these dynamic query operations, a more sophisticated indexing scheme is needed. In this paper, we present the Double Signature Indexing Scheme (DSIS) for a dynamic object-oriented database programming language with role extension, called DOOR. It supports retrievals of a large range of queries including class relation queries, nested queries as well as queries that exist only in dynamic environments like qualification and versioning queries. Query relaxation and specification are also supported by the index structure. We describe the index structure of the indexing scheme and show how the index structure supports dynamic operations as well as static operations. In addition, we present the operations of the indexing scheme and demonstrate how the operations of the new indexing mechanism handle different kind of queries.

Advanced object-oriented techniques for modeling robotic systems

To investigate the underlying principles of a robotic systems design and applications, appropriate specification and modeling tools which can facilitate the quantitative analysis as well as the qualitative analysis involving complex and/or dynamic data and relationships are essential. In this paper, advanced features embodied by dynamic role facilities have been introduced into a conventional object-oriented model, which facilitates the specification and modeling of robotic systems in a natural, incremental and systematic way. The model supports both the top-down and bottom-up design methodologies, as well as the computation of forward kinematics of the robots. With the analysis based on the communications among different roles, one can have further information about the cooperative behaviour and activities among multiple robots. The prototype system has been implemented in Lisp.

Manufacturing Systems Modeling with Roles: A Comprehensive Approach

Manufacturing systems for factory automation are large-scale ones in which enormous amount of data and operations are involved. In order to investigate the underlying principles of such systems, appropriate specification and modeling tools which can facilitate, besides the traditional quantitative analysis, the conceptual analysis involving complex and/or dynamic data and relationships are essential. This paper describes an object-oriented (O-O) approach that we have been investigating for this purpose. Advanced features embodied by dynamic role facilities have been introduced into a conventional object-oriented model, which facilitates specifying and modeling such applications in a natural, incremental and systematic way. Experimental prototype systems of the role mechanism have also been developed, which exploit different techniques and approaches of implementing roles, using either an O-O language with file system, or an existing O-O database system.