A temporal database contains time-varying data. In a real-time database transactions have deadlines or timing constraints. In this paper we review the substantial research in these two heretofore separate research areas. We first characterize the time domain, then investigate temporal and real-time data models. We evaluate temporal and real-time query languages along several dimensions. Temporal and real-time DBMS implementation is examined. We conclude with a summary of the major accomplishments of the research to date, and list several research questions that should be addressed next. Keywords: object-oriented database, relational databases, query language, temporal data model, time-constrained database, transaction time, user-defined time, valid time 1 Introduction Time is an important aspect of all real-world phenomena. Events occur at specific points in time; objects and the relationships among objects exist over time. The ability to model this temporal dimension of the real worl...

We describe the TIGUKAT objectbase management system that is under development at the Laboratory for Database Systems Research at the University of Alberta. TIGUKAT has a novel object model whose identifying characteristics include a purely behavioral semantics and a uniform approach to objects. Everything in the system, including types, classes, collections, behaviors, functions as well as meta-information, is a first-class object with well-defined behavior. In this way, the model abstracts everything, including traditional structural notions such as instance variables, method implementation and schema definition, into a uniform semantics of behaviors on objects. Our emphasis in this paper is on the object model, its implementation, the persistence model and the query language. We also (briefly) present other database management functions that are under development such as the query optimizer, the version control system and transaction manager.

1 Introduction A Formal Temporal Object-Oriented Data Model Elisa Bertino Elena Ferrari Giovanna Guerrini snapshot tuple timestamping attribute timestamping bertino@hermes.mc.dsi.unimi.it, ferrarie@dsi.unimi.it guerrini@disi.unige.it Temporal databases are an active and fast growing research area. Although many extensions to the relational data model have been proposed in order to incorporate time, there is no comparable amount of work in the context of object-oriented data models. This paper presents Chimera, a temporal extension of the Chimera object-oriented data model. The main contribution of this work is to define a formal temporal object-oriented data model and to address on a formal basis several issues deriving from the introduction of time in an object-oriented context. Dipartimento di Scienze dell'Informazione - Universit`a di Milano Via Comelico, 39/41 - I20133 Milano, Italy Dipartimento di Informatica e Scienze dell'Informazione - Universit`a di Genova Vi...

The schema of a system consists of the constructs that model its entities. Schema evolution is the timely change and management of the schema. Dynamic schema evolution is the management of schema changes while the system is in operation. We propose a sound and complete axiomatic model for dynamic schema evolution in objectbase management systems (OBMSs) that support subtyping and property inheritance. The model is formal, which distinguishes it from the traditional approach of informally defining a number of invariants and rules to enforce them. By reducing systems to the axiomatic model, their functionality with respect to dynamic schema evolution can be compared within a common framework. 1 Introduction Object-oriented computing is emerging as the predominant technology for providing database services in advanced application domains such as engineering design, CAD/CAM systems, multimedia, medical imaging, and geo-information systems, to name a few. An important characteristic of t...

Although many temporal extensions of the relational data model have been proposed, there is no comparable amount of work in the context of object-oriented data models. Moreover, extensions to the relational model have been proposed in the framework of SQL standards, whereas no attempts have been made to extend the standard for object-oriented databases, defined by ODMG. This paper presents T ODMG, a temporal extension of the ODMG-93 standard data model. The main contributions of this work are, thus, the formalization of the ODMG standard data model and its extension with time. Another contribution of this work is the investigation, on a formal basis, of the main issues arising from the introduction of time in an object-oriented model.

We describe the design of a multimedia database for a distributed news-on-demand multimedia information system. News-on-demand is an application that utilizes broadband network services to deliver news articles to subscribers in the form of multimedia documents. Different news providers insert articles into the database, which is then accessed by remote users over a broadband network. Multimedia documents are composite objects where the component objects have spatial and temporal relationships which need to be captured in the database. Modeling of multimedia documents involves three issues: (1) modeling of individual document components (i.e., monomedia objects such as text, images, etc), (2) modeling of the document structure, and (3) modeling of the presentation structure. We take an object-oriented approach to dealing with these issues. Within (1), our research has so far concentrated on text. We use an annotation based scheme where entire text is stored as a single document and th...

. Temporal DBMS offer concepts and functionalities related to data timestamping and history management. Analyzing the numerous approaches in this field demonstrate a significant lack of unification of the main results, thus postponing the emergence of commercial products. This problem is about to be solved for the relational approach, e.g. through the definition of the TSQL2 language. However, there is still much to be done in the context of object DBMS. This paper proposes an historical model integrating the main functionalities needed by an object DBMS to cope with the data historical dimensions. Key words: temporal databases, data history, temporal query object language, O2 . 1

In this paper we present a formal model for the support of temporal schema versions in object-oriented databases. Its definition is partially based on a generic (ODMG compatible) object model and partially introduces new concepts. The proposed model supports all the schema changes which are usually considered in the OODB literature, for which an operational semantics and a formal analysis of their correct behaviour is provided. Semantic issues arising from the introduction of temporal schema versioning in a conventional or temporal database (concerning the interaction between the intensional and extensional levels of versioning and the management of data in the presence of multiple schema versions) are also considered.

We present a temporal object model capable of representing the lifespan of objects and also the history of the roles and associations in which they participate. We advocate an approach of temporal generalisation rather than temporal extension in which a model in its entirety is given a temporal semantics through an orthogonal generalisation of all concepts of the model. Our model allows objects to participate in several roles simultaneously. Further, metadata may also have temporal properties allowing the lifespan of the object roles themselves, and constraints over these roles, to be modelled. The model is based on the generic object data model OM and the associated algebra has been generalised into a full temporal algebra over object roles.

. In OLAP models, or data cubes, aggregates have to be recalculated when the underlying base data changes. This may cause performance problems in real-time OLAP systems, which continuously accommodate huge amounts of measurement data. To optimize the aggregate computations, a new consistency criterion called the tolerance invariant is proposed. Lazy aggregates are aggregates that are recalculated only when the tolerance invariant is violated, i.e., the error of the previously calculated aggregate exceeds the given tolerance. An industrial case study is presented. The prototype implementation is described, together with the performance results. 1 Introduction Traditional OLAP (on-line analytical processing) [3] technology is developed mainly for commercial analysis needs. Data from various sources is compiled into multiattribute fact data tuples. They are used to compute multidimensional aggregates that make up the essence of OLAP. An industrial process is often a subject of ...