Approximate dependencies in database systems

Functional dependencies are the most commonly used approach for capturing real-word integrity constraints which are to be reflected in a database. There are, however, many useful kinds of constraints, especially approximate ones, that cannot be represented correctly by functional dependencies and therefore are enforced via programs which update the database, if they are enforced at all. This tends to make such constraints invisible since they are not an explicit part of the database, increasing maintenance problems and the likelihood of inconsistencies. We propose a new approach, cluster dependencies, as a way to enforce approximate dependencies. By treating equality as a fuzzy concept and defining appropriate similarity measures, it is possible to represent a broad range of approximate constraints directly in the database by storing and accessing cluster definitions. We discuss different interpretations of cluster dependencies and describe the additional data structures needed to enforce them. We also contrast them with an existing approach, fuzzy functional dependencies, which are much more limited in the kind of approximate constraints they can represent.     

Exploring into programs for the recovery of data dependenciesdesigned

Data dependencies play an important role in the design of a database. Many legacy database applications have been developed on old generation database management systems and conventional file systems. As a result, most of the data dependencies in legacy databases are not enforced in the database management systems. As such, they are not explicitly defined in database schema and are enforced in the transactions, which update the databases. It is very difficult and time consuming to find out the designed data dependencies manually during the maintenance and reengineering of database applications. In software engineering, program analysis has long been developed and proven as a useful aid in many areas. With the use of program analysis, this paper proposes a novel approach for the recovery of common data dependencies, i.e., functional dependencies, key constraints, inclusion dependencies, referential constraints, and sum dependencies, designed in a database from the behavior of transactions, which update the database. The approach is based on detecting program path patterns for implementing most commonly used methods to enforce these data dependencies     

The integrity constraints for similarity-based fuzzy relational databases

This paper first introduces a new definition for the conformance of tuples existing in a similarity-based fuzzy database relation. Then the formal definitions of fuzzy functional and multivalued dependencies are given on the basis of the conformance values presented here. These dependencies are defined to represent relationships between domains of the same relation that exist. The definitions of the fuzzy dependencies presented in this study allow a sound and complete set of inference rules. In this paper, we include examples to demonstrate how the integrity constraints imposed by these dependencies are enforced whenever a tuple is to be inserted or to be modified in a fuzzy database relation. © 1998 John Wiley & Sons, Inc.     

Independent database schemes under functional and inclusion dependencies

In a context considering in a unique framework all the relations in a database, by means of the notion of global consistency, independent database schemes allow enforcement of constraints to be performed locally, thus providing independent updatability of the various relations. Independent schemes have hitherto been studied in the presence of functional and join dependencies. In this paper the definition is extended and some characterizations are given for schemes whose sets of constraints contain functional and inclusion dependencies.An extended abstract of this paper appears in the Proceedings of the Thirteenth International Conference on Very Large Data Bases, Brighton, England, 1–4 September 1987, pp. 159–166. The work of the first author was supported byMinistero dell'Università e della Ricerca Scientifica e Tecnologica, within the Project Metodi formali e strumenti per basi di dati evolute and the work of the second author by the Natural Sciences and Engineering Research Council of Canada. Part of this work was performed when the first author was with IASI-CNR and then with Università di Napoli.     

A Logical Design Method for Relational Databases Based on Generalization and Aggregation Semantics

In this paper,a series of esign methods for relational databases based on generalization and aggregation semantics is set up.The relationship between a class and its subclass s considered as a scheme constraint.The concept of inheritance dependencies,which describes the multiple inheritance among schemes, is presented in the paper.It is shown that the inference rules for inheritance dependencies are sound and complete.Furthermore,a series of results about the closure of inheritance dependencies and the minimal set of inheritance dependencies,which are analogues to functional dependencies,is obtained.In order to describe the aggregation semantices,the concept of aggregation dependencies is given.It is easy to implement these constraints under relational database management systems.     

A note on lossless database decompositions

It is known that under a wide variety of assumptions a database decomposition is lossless if and only if the database scheme has a lossless join. Biskup, Dayal and Bernstein (1979) have shown that when the given dependencies are functional, the database scheme has a lossless join if and only if one of the relation schemes is a key for the universal scheme. In this note we supply an alternative proof of that characterization. The proof uses tools from the theory of embedded join dependencies and the theory of tuple and equality generating dependencies, but is, nevertheless, much simpler than the previously published proof.     

On characterizing boundedness of database schemes with bounded dependencies

We investigate the effect of bounded dependencies on the boundedness of database schemes. The following results are proved. A database scheme with only bounded equality-generating dependencies is always bounded with respect to dependencies; a lossless database scheme with bounded full implicational dependencies is bounded w.r.t. dependencies if and only if the implicational dependencies are equivalent to a single join dependency and some equality-generating dependencies. By a known method, this condition can be tested effectively. These results are relevant in database theory in that they determine in a rather general case whether queries under the representative instance approach can be expressed in relational algebra.     

Dependency preserving refinements and the fundamental problem of database design

We introduce a new point of view into database schemes by applying systematically an old logical technique: translation schemes, and their induced formula and structure transformations. This allows us to re-examine the notion of dependency preserving decomposition and its generalization refinement. We demonstrate the usefulness of this approach by recasting the theory of vertical and horizontal decompositions in our terminology. The most important aspect of this approach, however, lies in laying the groundwork for a formulation of the Fundamental Problem of Database Design, namely to exhibit desirable differences between translation equivalent presentations of data and to examine refinements of data presentations in a systematic way. The emphasis in this paper is not on results. The main line of thought is an exploration of the use of an old logical tool in addressing the Fundamental Problem. Translation schemes allow us also to have a new look at normal forms of database schemes and to suggest a new line of search for other normal forms. Illustrating our techniques we show that every scheme specified by functional and inclusion dependencies has a dependency-preserving refinement into BCNF. Furthermore we give a characterization of the embedded implicational dependencies (EID's) using FD's and inclusion dependencies (ID's) and a basic class of refinements consisting of projections and natural joins.     

Database survivability under dynamic constraints

Summary The connection between static constraints satisfied by a database and its future evolution under dynamic constraints is investigated using the notions of survivability and survivability-closure. The static constraints considered here are functional dependencies (fd’s). The dynamic constraints are restricted to commonly arising analogs of fd’s, called “dynamic” fd’s. The results provide new tools for the design of database schemes containing both static and dynamic constraints. Portions of this paper appeared in “Dynamic Constraints and Database Evolution”, Ph.D. Thesis, University of Southern California, 1983. The author was supported in part by the National Science Foundation under grant number MCS-7925004.     

Adequacy of decompositions of relational databases

We consider conditions that have appeared in the literature with the purpose of defining a “good” decomposition of a relation scheme. We show that these notions are equivalent in the case that all constraints in the database are functional dependencies. This result solves an open problem of Rissanen. However, for arbitrary constraints the notions are shown to differ.     

Representative Instances and ?-Acyclic Relational Schemes

In this paper, we study under what conditions will a pairwise inconsistent relational database ≪R,r≫ have a universal/representative instance L. If R is ?-acyclic and r satisfies all existence constraints, then it is possible to construct a universal instance L, using unmarked nulls, whose total projections onto R yield exactly the relations in r. We show that L would actually be a representative instance under a set of functional dependencies if R satisfies the additional mild condition: for any functional dependency X ? A where A is a single attribute, whenever XA is contained in two relation schemes R and R' of R, it follows that R ?R' is a relation scheme of R, having X as one of its keys.     

Transaction Management for Flash Media Databases in Portable Computing Environments

Flash memory is becoming a major database storage in building embedded systems or portable devices because of its non-volatile, shock-resistant, power-economic nature, and fast access time for read operations. Flash memory, however, should be erased before it can be rewritten and the erase and write operations are very slow as compared to main memory. Due to this drawback, traditional database management schemes are not easy to apply directly to flash memory database for portable devices. Therefore, we improve the traditional schemes and propose a new scheme called flash two phase locking (F2PL) scheme for efficient transaction processing in a flash memory database environment. F2PL achieves high transaction performance by exploiting the notion of the alternative version coordination which allows previous version reads and efficiently handles slow write/erase operations in lock management processes. We also propose a simulation model to show the performance of F2PL. Based on the results of the performance evaluation, we conclude that F2PL scheme outperforms the traditional schemes.     

Functional dependencies with null values, fuzzy values, and crispvalues

Based on the concepts of the semantic proximity, we present a definition of the fuzzy functional dependency, We show that the inference rules for fuzzy functional dependencies, which are the same as Armstrong's axioms for the crisp case, are correct and complete. We also show that dependent constraints with dull values constitute a lattice. Functional dependencies in classical relational databases and null functional dependencies can be viewed as a special case of fuzzy functional dependencies. By applying the unified functional dependencies to the relational database design, we can represent the data with fuzzy values, null values and crisp values under relational database management systems, By using fuzzy functional dependencies, we can compress the range of a fuzzy value and make this fuzzy value “clearer”     

具有全序时态类型集时态函数依赖集的研究

好的数据库逻辑设计目标是消除数据冗余以及插入、删除和更新异常.对于时态数据库,可以通过具有多时间粒度的时态函数依赖(TFDs)约束对时态数模式进行规范化.但是由于时间维的引入和多时间粒度的使用而给数据库设计带来巨大的复杂性.一般来说,系统所能处理的和相当多的应用所涉及到的时态类型集满足全序关系,并且具有全序时态类型集的TFD集的推导规则与传统函数依赖(FDs)的Armstrong公理有着紧密的联系.通过分析TFDs与FDs之间存在的联系,利用传统FD集的相应算法,提出了成员籍、有限属性闭包等TFD集的一些重要算法.这些算法是时态数据库进一步规范化的基础.     

On the Undecidability of Implications between Embedded Multivalued Database Dependencies

The implication and finite implication problems for embedded multivalued database dependencies are both shown to be algorithmically undecidable. The proof is by an interpretation of semigroup word problems via systems of permuting equivalence relations into database dependencies. In contrast, it is shown that for each fixed premise H one has a decision procedure for implications H F.     

具有多时间粒度的强全序时态模式中多值依赖问题研究

在时态数据库中存在着与时态多值依赖相关的存储冗余、更新异常等问题.但由于时态多值依赖的复杂性,使得根据时态多值依赖所进行的范式分解并不能总保持无损联接,为此对强全序时态模式中时态多值依赖与无损分解的相关性进行了深入研究,给出了规则的时态多值依赖(RTMVD)和属性集的时间粒度等概念,并给出了RTMVD的一套有效的推理规则,针对强全序时态模式中时态多值依赖与无损分解的相关性给出了相关定理,解决了规则的时态多值依赖环境下时态模式在多粒度上的无损分解问题,为规则时态多值依赖环境下时态模式的进一步规范化奠定了基础.     

Interval-based temporal functional dependencies: specification and verification

In the temporal database literature, every fact stored in a database may be equipped with two temporal dimensions: the valid time, which describes the time when the fact is true in the modeled reality, and the transaction time, which describes the time when the fact is current in the database and can be retrieved. Temporal functional dependencies (TFDs) add valid time to classical functional dependencies (FDs) in order to express database integrity constraints over the flow of time. Currently, proposals dealing with TFDs adopt a point-based approach, where tuples hold at specific time points, to express integrity constraints such as “for each month, the salary of an employee depends only on his role”. To the best of our knowledge, there are no proposals dealing with interval-based temporal functional dependencies (ITFDs), where the associated valid time is represented by an interval and there is the need of representing both point-based and interval-based data dependencies. In this paper, we propose ITFDs based on Allen’s interval relations and discuss their expressive power with respect to other TFDs proposed in the literature: ITFDs allow us to express interval-based data dependencies, which cannot be expressed through the existing point-based TFDs. ITFDs allow one to express constraints such as “employees starting to work the same day with the same role get the same salary” or “employees with a given role working on a project cannot start to work with the same role on another project that will end before the first one”. Furthermore, we propose new algorithms based on B-trees to efficiently verify the satisfaction of ITFDs in a temporal database. These algorithms guarantee that, starting from a relation satisfying a set of ITFDs, the updated relation still satisfies the given ITFDs.     

Polynomial Tests of Normal Forms and Some Related Results

The following problem is called the everywhere-cover problem:“Given a set of dependencies over a database scheme,is he set of dependencies explicitly given for each relation scheme equivalent to the dependencies implied for that relation sheme?”It is shown that when the everywhere-cover problem has a yes answer,examining only the dependencies explicitly given will suffice to test 3NF, BCNF and 4NF of a database scheme.But this does not hold for 2NF.Consequently,in such cases,tests of BCNF and 4NF all take polynomial time.Then a proof is given that test of 3NF of a database scheme is Co-NP-complete,and from this result it is shown that everywhere-cover is also Co-NP-complete when only functional dependencies are allowed.These results lead to doubt the truth of the well believed conjecture that no polynomial time algorithm for designing a lossless BCNF database scheme is likely to exist.     

Minimal-change integrity maintenance using tuple deletions

We address the problem of minimal-change integrity maintenance in the context of integrity constraints in relational databases. We assume that integrity-restoration actions are limited to tuple deletions. We focus on two basic computational issues: repair checking (is a database instance a repair of a given database?) and consistent query answers [in: ACM Symposium on Principles of Database Systems (PODS), 1999, 68] (is a tuple an answer to a given query in every repair of a given database?). We study the computational complexity of both problems, delineating the boundary between the tractable and the intractable cases. We consider denial constraints, general functional and inclusion dependencies, as well as key and foreign key constraints. Our results shed light on the computational feasibility of minimal-change integrity maintenance. The tractable cases should lead to practical implementations. The intractability results highlight the inherent limitations of any integrity enforcement mechanism, e.g., triggers or referential constraint actions, as a way of performing minimal-change integrity maintenance.     

Functional and multivalued dependencies in nested databases generated by record and list constructor

The impact of the list constructor on two important classes of relational dependencies is investigated. Lists represent an inevitable data structure whenever order matters and data is allowed to occur repeatedly. The list constructor is therefore supported by many advanced data models such as genomic sequence, deductive and object-oriented data models including XML. The article proposes finite axiomatisations of functional, multivalued and both functional and multivalued dependencies in nested databases supporting record and list constructor. In order to capture different data models at a time, an abstract algebraic approach based on nested attributes is taken. The presence of the list constructor calls for a new inference rule which allows to infer non-trivial functional dependencies from multivalued dependencies. Further differences to the relational theory become apparent when the independence of the inference rules is investigated. The extension of the relational theory to nested databases allows to specify more real-world constraints and increases therefore the number of application domains. * Results of this article were partly presented at the 3rd International Symposium on Foundations of Information and Knowledge Systems (FoIKS), Vienna, Austria, 2004 [58], and the 23rd International Symposium on Principles of Database Systems (PODS), Paris, France, 2004 [54]. ** Sebastian Link was supported by Marsden Funding, Royal Society of New Zealand.