A transparent schema-evolution system based on object-oriented viewtechnology

When a database is shared by many users, updates to the database schema are almost always prohibited because there is a risk of making existing application programs obsolete when they run against the modified schema. The paper addresses the problem by integrating schema evolution with view facilities. When new requirements necessitate schema updates for a particular user, then the user specifies schema changes to his personal view, rather than to the shared base schema. Our view schema evolution approach then computes a new view schema that reflects the semantics of the desired schema change, and replaces the old view with the new one. We show that our system provides the means for schema change without affecting other views (and thus without affecting existing application programs). The persistent data is shared by different views of the schema, i.e., both old as well as newly developed applications can continue to interoperate. The paper describes a solution approach of realizing the evolution mechanism as a working system, which as its key feature requires the underlying object oriented view system to support capacity augmenting views. We present algorithms that implement the complete set of typical schema evolution operations as view definitions. Lastly, we describe the transparent schema evolution system (TSE) that we have built on top of GemStone, including our solution for supporting capacity augmenting view mechanisms     

Database application evolution: A transformational approach

While recent data management technologies, such as object oriented techniques, address the problem of database schema evolution, standard information systems currently in use raise challenging evolution problems. This paper examines database evolution from the developer point of view. It shows how requirements changes are propagated to database schemas, to data and to programs through a general strategy. This strategy requires the documentation of database design. When absent, such documentation has to be rebuilt through reverse engineering techniques. Our approach, called DB-MAIN, relies on a generic database model and on transformational paradigm that states that database engineering processes can be modeled by schema transformations. Indeed, a transformation provides both structural and instance mappings that formally define how to modify database structures and contents. We describe both the complete and a simplified approaches, and compare their merits and drawbacks. We then analyze the problem of program modification and describe a CASE tool that can assist developers in their task of system evolution. We illustrate our approach with Biomaze, a biochemical knowledge-based the database of which is rapidly evolving.     

Computing access relevance for path-method generation in OODB and IM-OODB

A path-method (PM) is a mechanism to retrieve or to update information relevant to one class, in an object-oriented database (OODB), that is not stored with that class but with some other class. The PM traverses a chain of classes and connections that ends at the class where the required information is stored. However, it is a difficult task for a user to write PMs. This is because it might require comprehensive knowledge of many classes of the conceptual schema. But a typical user has often incomplete or even inconsistent knowledge of the schema. Currently we are developing a system, called Path-Method Generator (PMG), which generates PMs automatically according to a naive user's requests. One algorithm of PMG uses numerical access relevance between pairs of classes as a guide for the traversal of an OODB schema. In this paper we define the notion of access relevance to measure the significance of the (indirect) connection between any two classes in an OODB and present efficient algorithms to compute access relevance. The manual PM generation in an interoperable multi object-oriented database (IM-OODB) is even more difficult than for one OODB since a user has to be familiar with several OODBs. We use a hierarchical approach for developing efficient online algorithms for the computation of access relevances in an IM-OODB, based on precomputed access relevances for each autonomous OODB. In an IM-OODB the access relevances are used as a guide in generating PMs between the classes of different OODBs.     

Schema evolution of an object-oriented real-time database systemfor manufacturing automation

Database schemata often experience considerable changes during the development and initial use phases of database systems for advanced applications such as manufacturing automation and computer-aided design. An automated schema evolution system can significantly reduce the amount of effort and potential errors related to schema changes. Although schema evolution for nonreal-time databases was the subject of previous research, its impact on real-time database systems remains unexplored. These advanced applications typically utilize object-oriented data models to handle complex data types. However, there exists no agreed-upon real-time object-oriented data model that can be used as a foundation to define a schema-evolution framework. Therefore, the authors first design a conceptual real-time object-oriented data model, called Real-time Object Model with Performance Polymorphism (ROMPP). It captures the key characteristics of real-time applications-namely, timing constraints and performance polymorphism-by utilizing specialization-dimension and letter-class hierarchy constructs, respectively. They then re-evaluate previous (nonreal-time) schema evolution support in the context of real-time databases. This results in modifications to the semantics of schema changes and to the needs of schema change resolution rules and schema invariants. Furthermore, they expand the schema change framework with new constructs-including new schema change operators, new resolution rules, and new invariants-necessary for handling the real-time characteristics of ROMPP     

A formal perspective on the view selection problem

The view selection problem is to choose a set of views to materialize over a database schema, such that the cost of evaluating a set of workload queries is minimized and such that the views fit into a prespecified storage constraint. The two main applications of the view selection problem are materializing views in a database to speed up query processing, and selecting views to materialize in a data warehouse to answer decision support queries. In addition, view selection is a core problem for intelligent data placement over a wide-area network for data integration applications and data management for ubiquitous computing. We describe several fundamental results concerning the view selection problem. We consider the problem for views and workloads that consist of equality-selection, project and join queries, and show that the complexity of the problem depends crucially on the quality of the estimates that a query optimizer has on the size of the views it is considering to materialize. When a query optimizer has good estimates of the sizes of the views, we show a somewhat surprising result, namely, that an optimal choice of views may involve a number of views that is exponential in the size of the database schema. On the other hand, when an optimizer uses standard estimation heuristics, we show that the number of necessary views and the expression size of each view are polynomially bounded. Received: November 20, 1001 / Accepted: May 30, 2002 / Published online: September 25, 2002     

Conceptual database evolution through learning in object databases

Changes to the conceptual structure (meta-data) of a database are common in many application environments and are in general inadequately supported by existing database systems. An approach to supporting such meta-data evolution in a simple, extensible, object database environment is presented. Machine learning techniques are the basis for a cooperative user/system database design and evolution methodology. An experimental end-user database evolution tool based on this approach has been designed and implemented     

A composite approach to automating direct and indirect schema mappings

Automating schema mapping is challenging. Previous approaches to automating schema mapping focus mainly on computing direct matches between two schemas. Schemas, however, rarely match directly. Thus, to complete the task of schema mapping, we must also compute indirect matches. In this paper, we present a composite approach for generating a source-to-target mapping that contains both direct and many indirect matches between a source schema and a target schema. Recognizing expected-data values associated with schema elements and applying schema-structure heuristics are the key ideas needed to compute indirect matches. Experiments we have conducted over several real-world application domains show encouraging results, yielding about 90% precision and recall measures for both direct and indirect matches.     

基于路径无关语言的等价模式演化策略

面向对象数据库的许多应用环境需要频繁的模式演以化,但模式演化以后,基于先前模式的应用程序因此而不得不修改或重编,这就造成了巨大的软件浪费.提出了基于路径无关语言的等价模式演化方案来解决这个问题.首先,路径无关语言是一种面向对象数据库的编程语言,它能使程序脱离对细节数据模式的导航,对模式演化具有较强的适应性.而等价模式演化是一种新的模式演化方案,它能保证用路径无关语言编写的应用程序在模式演化以后无须修改而完全重用.此外,在实现等价模式演化的系统中,为了减少演化开销以及不增加用户的额外编程负担,提出了虚拟关系机制和对象演化技术.     

A multiagent update process in a database with temporal datadependencies and schema versioning

Temporal data dependencies are high-level linguistic constructs that define relationships among values of data-elements in temporal databases. These constructs enable the support of schema versioning as well as the definition of consistency requirements for a single time-point and among values in different time-points. In this paper, we present a multiagent update process in a database with temporal data dependencies and schema versioning. The update process supports the evolution of dependencies over time and the use of temporal operators within temporal data dependencies. The temporal dependency language is presented, along with the temporal dependency graph-which serves as the executable data structure. A thorough discussion of the feasibility, performance, and consistency of the presented model is provided     

An environmental evaluation learning apprentice system

In engineering problems with a weak domain theory, such as environmental evaluation, machine learning techniques should bring to bear any existing background knowledge so as to guide the knowledge-acquisition process. This paper proposes an Interactive Inductive Learning System (IILS) which can use background knowledge provided by experts to avoid incorrect or incomplete induced heuristics. Through the specification of guidance relations, the expert can force the rule-induction system to focus on a subset of relevant attributes and training instances. A guidance relation consists of a set of attribute constraints, where each constraint instructs IILS on the role of an attribute for the induction of a concept. IILS has been linked to the database of an Environmental Evaluation Support System (EESS) for the induction of impact estimation and comparison heuristics. The induced heuristics are generalizations of past assessments stored in the database and permit the prediction of impact levels for cases not previously encountered by EESS. The integration of IILS transforms EESS into an environmental impact assessment learning apprentice system capable of acquiring and improving evaluation heuristics through its normal use.     

An Object Algebra Approach to Multidatabase Query Decomposition in Donají

This paper presents an approach to query decomposition in a multidatabase environment. The unique aspect of this approach is that it is based on performing transformations over an object algebra that can be used as the basis for a global query language. In the paper, we first present our multidatabase environment and semantic framework, where a global conceptual schema based on the Object Data Management Group standard encompasses the information from heterogeneous data sources that include relational databases as well as object-oriented databases and flat file sources. The meta-data about the global schema is enhanced with information about virtual classes as well as virtual relationships and inheritance hierarchies that exist between multiple sources. The AQUA object algebra is used as the formal foundation for manipulation of the query expression over the multidatabase. AQUA is enhanced with distribution operators for dealing with data distribution issues. During query decomposition we perform an extensive analysis of traversals for path expressions that involve virtual relationships and hierarchies for access to several heterogeneous sources. The distribution operators defined in algebraic terms enhance the global algebra expression with semantic information about the structure, distribution, and localization of the data sources relevant to the solution of the query. By using an object algebra as the basis for query processing, we are able to define algebraic transformations and exploit rewriting techniques during the decomposition phase. Our use of an object algebra also provides a formal and uniform representation for dealing with an object-oriented approach to multidatabase query processing. As part of our query processing discussion, we include an overview of a global object identification approach for relating semantically equivalent objects from diverse data sources, illustrating how knowledge about global object identity is used in the decomposition and assembly processes.     

A Graph-Rewriting Visual Language for Database Programming

Textual database programming languages are computationally complete, but have the disadvantage of giving the user a non-intuitive view of the database information that is being manipulated. The visual languages developed in recent years have allowed naive users access to a direct representation of data, often in a graph form, but have concentrated on user interface rather than complex programming tasks. There is a need for a system which combines the advantages of both these programming methods.We describe an implementation of Spider, an experimental visual database programming language aimed at programmers. It uses a graph-rewriting paradigm as a basis for a fully visual, computationally complete language. The graphs it rewrites represent the schema and instances of a database.The unique graph-rewriting method used by Spider has syntactic and semantic simplicity. Its form of algorithmic expression allows complex computation to be easily represented in short programs. Furthermore, Spider has greater power than normally provided in textual systems, and we show that queries on the schema and associative queries can be performed easily and without requiring any additions to the language.     

Schema evolution and integration

Providing support forschema evolution allows existing databases to be adjusted for varying roles over time. This paper reflects on existing evolution support schemes and introduces a more general and functional mechanism to support schema evolution andinstance adaptation for centralized and distributed object-oriented database systems. Our evolution support scheme is distinguished from previous mechanisms in that it is primarily concerned with preserving existing database objects and maintaining compatibility for old applications, while permitting a wider range of evolution operations. It achieves this by supporting schema versioning, allowing multiple representations of instances to persist simultaneously, and providing for programmer specification of how to adapt existing instances. The mechanism is general enough to provide much of the support necessarily forheterogeneous schema integration, as well as incorporating much of the features of object migration and replication.     

Foundations of entity-relationship modeling

Database design methodologies should facilitate database modeling, effectively support database processing, and transform a conceptual schema of the database to a high-performance database schema in the model of the corresponding DBMS. The Entity-Relationship Model is extended to theHigher-orderEntity-RelationshipModel (HERM) which can be used as a high-level, simple and comprehensive database design model for the complete database information on the structure, operations, static and dynamic semantics. The model has the expressive power of semantic models and possesses the simplicity of the entity-relationship model. The paper shows that the model has a well-founded semantics. Several semantical constraints are considered for this model.     

Invisible Work of Telephone Operators: An Ethnocritical Analysis

This paper applies principles derived from ethnocriticism to help explain differential outcomes with different methods used to analyze the work of Directory Assistance telephone operators in a large US telecommunications company. The work of Directory Assistance operators provides a subtle case of computer-supported cooperative work. Collaborative work between operator and customer is supported and shaped by digitized-voice and database technologies. Our work also involved the introduction of additional voice-recognition technologies to this human-to-human collaboration. In a previous paper, we used methods from participatory design to show that knowledge work is a major component of the operators' conversations with customers. By contrast, other research using formal cognitive task analyses had described operators' work as routine and as involving no active problem solving. How had evidence that we had found so compelling been invisible to other analysts? I analyze the concept of “invisible work” as an attribute not of the work, but rather of the perspectives from which that work appeared to be invisible. Ethnocritical heuristics help us to contrast the analytical methods and their outcomes.     

Managing schema evolution in a container‐based persistent system

Managing schema evolution is a problem every persistent system has to cope with to be useful in practice. Schema evolution consists basically of supporting class modification and dealing with data objects created and stored under the old class definitions. Several proposals have been made to handle this problem in systems that follow a full orthogonally persistent approach, but, until now, there has not been any proposal to support it in container‐based persistent systems. In this paper we describe a schema evolution management system designed for Barbados. Barbados is a complete programming environment which is based on an architecture of containers to provide persistent storage. Barbados does not provide full orthogonal persistence, but, as will be described in this paper, its architecture has several other advantages. Among them is the fact that this model is especially suitable for solving the schema evolution problem. Copyright © 2002 John Wiley & Sons, Ltd.     

Combining knowledge with many-valued logics

We compare EER and OO data models from the point of view of design quality. Quality is measured in terms of (a) correctness of the conceptual schemas being designed, (b) time to complete the design task, and (c) designers' preferences of the models. Result of an experimental comparison of the two models reveal that the EER model surpasses the OO model for designing unary and ternary relationships, it takes less time to design EER schemas, and the EER model is preferred by designers. We conclude that even if the objective is to implement an OO database schema, the recommended procedure is to: (1) create an EER conceptual scheme, (2) map it to an OO schema, and augment the target schema with behavioral constructs that are unique to the OO approach.