Approaching Distributed Database Implementations Through Functional Programming Concepts

The application of functional programming concepts to the data representation and querying aspects of databases has been discussed by Shipman and Buneman, et al. respectively. We argue the suitability of a function-based approach to additional aspects of database systems, including updating, transaction serialization, and physical distribution and communication. It is shown how the NmergeH extension of a purely functional model permits serializable concurrent primary site distribution control. We also present preliminary experimental results which indicate that a reasonable degree of concurrency is attainable from the functional approach

Incorporating record subtyping into a relational data model

Most of the current proposals for new data models support the construction of heterogeneous sets. One of the major challenges for such data models is to provide strong typing in the presence of heterogenity. Therefore the inclusion of as much as possible information concerning legal structural variants is needed. We argue that the shape of some part of a heterogeneous scheme is often determined by the contents of some other part of the scheme. This relationship can be formalized by a certain type of integrity constraint we have called attribute dependency. Attribute dependencies combine the expressive power of general sums with a notation that fits into relational models. We show that attribute dependencies can be used, besides their application in type and integrity checking, to incorporate record subtyping into a relational model. Moreover, the notion of attribute dependency yields a stronger assertion than the traditional record subtyping rule as it considers some refinements to be caused by others. To examine the differences between attribute dependencies and traditional record subtyping and to be able to predict how attribute dependencies behave under transformations like query language operations we develop an axiom system for their derivation and prove it to be sound and complete. We further investigate the interaction between functional and attribute dependencies and examine an extended axiom system capturing both forms of dependencies

Canonical queries as a query answering device (Information Science)

Issued as Annual reports [nos. 1-2], and Final report, Project no. G-36-60

Integration of Heterogeneous Databases: Discovery of Meta-Information and Maintenance of Schema-Restructuring Views

In today\u27s networked world, information is widely distributed across many independent databases in heterogeneous formats. Integrating such information is a difficult task and has been adressed by several projects. However, previous integration solutions, such as the EVE-Project, have several shortcomings. Database contents and structure change frequently, and users often have incomplete information about the data content and structure of the databases they use. When information from several such insufficiently described sources is to be extracted and integrated, two problems have to be solved: How can we discover the structure and contents of and interrelationships among unknown databases, and how can we provide durable integration views over several such databases? In this dissertation, we have developed solutions for those key problems in information integration. The first part of the dissertation addresses the fact that knowledge about the interrelationships between databases is essential for any attempt at solving the information integration problem. We are presenting an algorithm called FIND2 based on the clique-finding problem in graphs and k-uniform hypergraphs to discover redundancy relationships between two relations. Furthermore, the algorithm is enhanced by heuristics that significantly reduce the search space when necessary. Extensive experimental studies on the algorithm both with and without heuristics illustrate its effectiveness on a variety of real-world data sets. The second part of the dissertation addresses the durable view problem and presents the first algorithm for incremental view maintenance in schema-restructuring views. Such views are essential for the integration of heterogeneous databases. They are typically defined in schema-restructuring query languages like SchemaSQL, which can transform schema into data and vice versa, making traditional view maintenance based on differential queries impossible. Based on an existing algebra for SchemaSQL, we present an update propagation algorithm that propagates updates along the query algebra tree and prove its correctness. We also propose optimizations on our algorithm and present experimental results showing its benefits over view recomputation

Анализ типизированных зависимостей включения с неопределенными значениями

Null values have become an urgent problem since the creation of the relational data model. The impact of the uncertainty affects all types of dependencies used in the design and operation of the database. This fully applies to the inclusion dependencies, which are the theoretical basis for referential integrity on the data. Attempts to solve this problem contain inaccuracy in the statement of the problem and its solution. The errors in formulation of the problem can be associated with the use in the definition of untyped inclusion dependencies, which leads to permutations of the attributes, although, the attributes in database technology are identified by name and not by their place. In addition, linking with the use of the inclusion dependencies of heterogeneous attributes, even of the same type, is a sign of lost functional dependencies and leads to interaction of inclusion dependencies and non-trivial functional dependencies. Inaccuracies in the solution of the problem are contained in the statements of axioms and the proof of their properties, including completeness. In this paper we propose an original solution of this problem only for typed inclusion dependencies in the presence of Null values: a new axiom system is proposed, its completeness and soundness are proved. On the basis of inference rules we developed an algorithm for the construction of a not surplus set of typed inclusion dependencies. The correctness of the algorithm is proved.Неопределенные значения стали актуальной проблемой с момента создания реляционной модели данных. Влияние неопределенностей сказывается на всех видах зависимостей, используемых при проектировании и эксплуатации базы данных. В полной мере это относится и к зависимостям включения, которые являются теоретической основой ссылочной целостности на данные. Попытки решения указанной проблемы содержат неточности как в постановке задачи, так и в самом ее решении. К постановочным ошибкам можно отнести использование в определении нетипизированных зависимостей включения, что приводит к перестановкам атрибутов, хотя в технологиях баз данных атрибуты идентифицируются по имени, а не по их позиции. Кроме того, связывание зависимостью включения разнородных, пусть даже однотипных, атрибутов является признаком потерянной функциональной зависимости и приводит к взаимодействию нетривиальных зависимостей включения и функциональных зависимостей. Зависимости включения должны определять количественное соотнесение объектов друг с другом, а не значений атрибутов. Неточности в решении указанной проблемы содержатся в формулировках аксиом и доказательстве их свойств, в том числе полноты. В этой статье предлагается оригинальное решение этой проблемы только для типизированных зависимостей включения при наличии неопределенных значений: предложена система аксиом, доказана ее полнота и непротиворечивость. На основе правил вывода разработан алгоритм построения не избыточного множества типизированных зависимостей включения. Доказана корректность этого алгоритма

An approach to modeling database activity

Results in the field of data modeling currently suffer from many of the same ills which plagued data management systems in the late 1960's. Advanced semantic modeling systems such as the Semantic Data Model and the Relational Model/Tasmania are extremely complex to understand as well as somewhat ad hoc in design. Such systems capture only static snapshots of activity in the world being modeled. On the other hand, behavioral models which do attempt to model system dynamics typically provide less overall modeling power than comprehensive semantic models. Further, the specifications of behavior which can be expressed with such models are themselves static snapshots which are not integrated with other database objects.This work describes one approach for capturing dynamic relationships by distilling the concepts found in semantic and behavioral data models into a small number of flexible constructs. The resulting Prototype Activity Modeling System (PAMS) captures the containment, feedback, operational, and state dependency roles of entities in the world being modeled. Further, these definitions of database activity are captured as database objects (rather than as a schema) so as to allow dynamic manipulation of entity roles.The key concept of the approach is the bundle - a purposefully designed extension of time-proven relational database modeling concepts which includes support for presentation ordering and complex Cartesian aggregations. By applying the basic nested bundle principle, it is possible to obtain complex hierarchies of static structural information. The static templates so constructed, when used with a non-procedural query language and the value nomination principle which reduces relations to scalar values when necessary, provide a conventional database modeling system for applications. By extending these templates with the non-procedural thunk principle which embeds query specifications within object definitions, variations caused by dependencies within the application can cause the apparent contents of the database description to change. When further extended by the activity monitoring principle which records the interaction between the application and its environment, these dynamic templates can account for changes outside the scope of the application

Four Lessons in Versatility or How Query Languages Adapt to the Web

Exposing not only human-centered information, but machine-processable data on the Web is one of the commonalities of recent Web trends. It has enabled a new kind of applications and businesses where the data is used in ways not foreseen by the data providers. Yet this exposition has fractured the Web into islands of data, each in different Web formats: Some providers choose XML, others RDF, again others JSON or OWL, for their data, even in similar domains. This fracturing stifles innovation as application builders have to cope not only with one Web stack (e.g., XML technology) but with several ones, each of considerable complexity. With Xcerpt we have developed a rule- and pattern based query language that aims to give shield application builders from much of this complexity: In a single query language XML and RDF data can be accessed, processed, combined, and re-published. Though the need for combined access to XML and RDF data has been recognized in previous work (including the W3C’s GRDDL), our approach differs in four main aspects: (1) We provide a single language (rather than two separate or embedded languages), thus minimizing the conceptual overhead of dealing with disparate data formats. (2) Both the declarative (logic-based) and the operational semantics are unified in that they apply for querying XML and RDF in the same way. (3) We show that the resulting query language can be implemented reusing traditional database technology, if desirable. Nevertheless, we also give a unified evaluation approach based on interval labelings of graphs that is at least as fast as existing approaches for tree-shaped XML data, yet provides linear time and space querying also for many RDF graphs. We believe that Web query languages are the right tool for declarative data access in Web applications and that Xcerpt is a significant step towards a more convenient, yet highly efficient data access in a “Web of Data”