Database Query Language Research Articles

Barcelona, Spain, October 7-8, 2002: Graph-Based Tools (GraBaTs 2002)

Barcelona, Spain, October 7-8, 2002: Graph-Based Tools (GraBaTs 2002)

Adding a path connectedness operator to FO+poly ( linear )

In the constraint database community FO+poly and FO+linear have been proposed as foundations for spatial database query languages. One of the strengths of this approach is that these languages are a clean and natural generalization of Codd's relational model to a spatial setting. As a result rigorous mathematical study of their expressiveness and complexity can be carried out.

An abbreviated concept-based query language and its exploratory evaluation

Research on the use of conceptual information in database queries has primarily focused on semantic query optimization. Studies on the important aspects of conceptual query formulation are currently not as extensive. Only a relatively small number of works exist in this area. The existing concept-based query languages are similar in the sense that they require the user to specify the entire query path in formulating a query. In this study, we present the Conceptual Query Language (CQL), which does not require entire query paths to be specified but only their terminal points. CQL is an abbreviated concept-based query language that allows for the conceptual abstraction of database queries and exploits the rich semantics of semantic data models to ease and facilitate query formulation. CQL was developed with the aim of providing typical end-users like secretaries and administrators an easy-to-use database query interface for querying and report generation. A CQL prototype has been implemented and currently runs as a front-end to an underlying relational DBMS. A statistical experiment conducted to probe end-users' reaction to using CQL vis-à-vis SQL as a database query language indicates that end-users perform better with CQL and have a better perception of it than of SQL. This paper discusses the design of CQL, the strategies for CQL query processing, and the comparative study between CQL and SQL.

Implementation of the Prometheus Taxonomic Model: a comparison of database models and query languages and an introduction to the Prometheus Object­Oriented Model

AbstractTypes of databases commonly used for handling taxonomic data are compared. It is shown that none of the existing types of databases fully support the requirements of taxonomic data. The results of this comparison provide a rationale for the design and implementation of a new database system based on an Extended Object­Oriented model. The new model, the Prometheus Object­Oriented Model (POOM) and its query language Prometheus Object­Oriented Language (POOL), are discussed in relation to the requirements of taxonomic data and the Prometheus Taxonomic Data Model. POOM provides the ability to represent the semantics of relationships between data. This allows us to build the type of graph structures that are found in taxonomic hierarchies. In addition, the system can query and manipulate these graphs (POOL). These features have been used to improve the original Prometheus Taxonomic Data Model. These improvements and the advantages they offer are described and discussed.

Towards a Declarative Query and TransformationLanguage for XML and Semistructured Data:Simulation Unification

The growing importance of XML as a data interchange standard demands languages for data querying and transformation. Since the mid 90es, several such languages have been proposed that are inspired from functional languages (such as XSLT [1]) and/or database query languages (such as XQuery [2]). This paper addresses applying logic programming concepts and techniques to designing a declarative, rule-based query and transformation language for XML and semistructured data. The paper first introduces issues specific to XML and semistructured data such as the necessity of flexible “query terms” and of “construct terms”. Then, it is argued that logic programming concepts are particularly appropriate for a declarative query and transformation language for XML and semistructured data. Finally, a new form of unification, called “simulation unification”, is proposed for answering “query terms”, and it is illustrated on examples.

Efficient Querying and Animation of Periodic Spatio-Temporal Databases

We propose a representation of spatio-temporal objects with continuous and cyclic or acyclic periodic movements. We also describe an extended relational algebra query language for databases with such objects. We show that the new spatio-temporal databases are closed under the extended relational algebra queries, and each fixed relational algebra query can be evaluated in PTIME in the size of the input database.

Design and implementation of spatiotemporal database query processing system

Researches on spatial and temporal databases have been done independently. In terms of spatial databases, whenever a new object instance is inserted into a database, the old one should be deleted. It stands for the difficulty to manage efficiently the historical information about spatial object that has been changed with temporal evolution. In view of temporal databases, because it did not consider supporting spatial type and operation, it is extremely hard to manage directly spatial objects without any modification. Nevertheless, because these research domains are closely related, an integration field, i.e., spatiotemporal databases, has been launched. Spatiotemporal databases support historical information as well as spatial management for the object at the same time and can deal with geometries changing over time. They can be used in the various application areas such as geographic information system (GIS), urban plan system (UPS), and car navigation system (CNS), and so on. In this paper, we design not only the spatiotemporal query processing (STQP) system, but also implement them. They include a spatiotemporal data model (STDM) that supports bitemporal concept for spatial objects. We also explain a specification of the spatiotemporal database query language, entitled as STQL as well. Compared with the results of the previous researches, we insist that it is the first pilot system in the spatiotemporal database area that supports temporal concept and spatial expression as well.

The effects of information request ambiguity and construct incongruence on query development

This paper examines the effects of information request ambiguity and construct incongruence on end user's ability to develop SQL queries with an interactive relational database query language. In this experiment, ambiguity in information requests adversely affected accuracy and efficiency. Incongruities among the information request, the query syntax, and the data representation adversely affected accuracy, efficiency, and confidence. The results for ambiguity suggest that organizations might elicit better query development if end users were sensitized to the nature of ambiguities that could arise in their business contexts. End users could translate natural language queries into pseudo-SQL that could be examined for precision before the queries were developed. The results for incongruence suggest that better query development might ensue if semantic distances could be reduced by giving users data representations and database views that maximize construct congruence for the kinds of queries in typical domains.

Enriching the conceptual basis for query formulation through relationship semantics in databases

The rapid increase in end-user computing calls into question the suitability of existing database query languages (DBQLs). Because the typical DB end-user is not a DB specialist, it is essential that DBQLs use concepts that are as close as possible to those in the end-users’ cognitive mental model and adopt interface techniques that are suited to end-users’ abilities. Concept-based query languages are well suited for this. This realization has motivated further research in conceptual, or semantic, query approaches. However, the primary focus in this field has been on semantic query optimization, not on query formulation. In this study, we address ourselves to the problem of formulation of queries using concepts. We propose a concept-based query language, called the conceptual query language (CQL), which allows for the conceptual abstraction of database queries and exploits the rich semantics of data models to ease and facilitate query formulation. The CQL approach uses the relationship semantics of semantic data models to render transparent the technical complexities of existing DB query languages. Association semantics are also used to automatically construct query graphs and pseudo-natural language explanations of queries, and to generate SQL codes. A set theoretic formalism for conceptual queries is developed and used. This paper discusses the design of CQL, its expressive power, its implementation, and the strategies for CQL query processing. The implementation of a CQL prototype is briefly discussed in this paper. User experiments were carried out extensively and showed the advantage of CQL over alternative languages such as SQL.

Logics with aggregate operators

We study adding aggregate operators, such as summing up elements of a column of a relation, to logics with counting mechanisms. The primary motivation comes from database applications, where aggregate operators are present in all real life query languages. Unlike other features of query languages, aggregates are not adequately captured by the existing logical formalisms. Consequently, all previous approaches to analyzing the expressive power of aggregation were only capable of producing partial results, depending on the allowed class of aggregate and arithmetic operations.We consider a powerful counting logic, and extend it with the set of all aggregate operators. We show that the resulting logic satisfies analogs of Hanf's and Gaifman's theorems, meaning that it can only express local properties. We consider a database query language that expresses all the standard aggregates found in commercial query languages, and show how it can be translated into the aggregate logic, thereby providing a number of expressivity bounds, that do not depend on a particular class of arithmetic functions, and that subsume all those previously known. We consider a restricted aggregate logic that gives us a tighter capture of database languages, and also use it to show that some questions on expressivity of aggregation cannot be answered without resolving some deep problems in complexity theory.

On the expressiveness of linear-constraint query languages for spatial databases

The linear database model, in which semi-linear sets are the only geometric objects, has been identified as suitable for spatial database applications from both modeling expressiveness as query efficiency considerations. For querying linear databases, the language FO+ linear has been proposed. In this paper, we examine the expressiveness of this language. First, we present a list of general queries expressible in FO+ linear . In particular, we mention the dimension query, which in turn allows us to express several other interesting linear queries. Next, we show the non-expressibility in FO+ linear of a whole class of linear queries that are related to sets not definable by linear formulae, a result which demonstrates the need for more expressive linear query languages. We present a method to extend FO+ linear with operators in a sound way with respect to the linear queries expressible in FO+ poly , and argue its validity by comparing it to another paradigm for enriching FO+ linear . Whether any of the proposed extensions is complete for the linear queries definable in FO+ poly remains open.

Preference queries in deductive databases

Traditional database query languages such as datalog and SQL allow the user to specify only mandatory requirements on the data to be retrieved from a database. In many applications, it may be natural to express not only mandatory requirements but also preferences on the data to be retrieved. Lacroix and Lavency10) extended SQL with a notion of preference and showed how the resulting query language could still be translated into the domain relational calculus. We explore the use of preference in databases in the setting of datalog. We introduce the formalism of preference datalog programs (PDPs) as preference logic programs without uninterpreted function symbols for this purpose. PDPs extend datalog not only with constructs to specify which predicate is to be optimized and the criterion for optimization but also with constructs to specify which predicate to be relaxed and the criterion to be used for relaxation. We can show that all of the soft requirements in Reference10) can be directly encoded in PDP. We first develop anaively-pruned bottom-up evaluation procedure that is sound and complete for computing answers to normal and relaxation queries when the PDPs are stratified, we then show how the evaluation scheme can be extended to the case when the programs are not necessarily stratified, and finally we develop an extension of themagic templates method for datalog14) that constructs an equivalent but more efficient program for bottom-up evaluation.

Query languages for sequence databases: termination and complexity

This paper develops a query language for sequence databases, such as genome databases and text databases. Unlike relational data, queries over sequential data can easily produce infinite answer sets since the universe of sequences is infinite, even for a finite alphabet. The challenge is to develop query languages that are both highly expressive and finite. This paper develops such a language as a subset of a logic for string databases called Sequence Datalog. The main idea is to use safe recursion to control and limit unsafe recursion. The main results are the definition of a finite form of recursion, called domain-bounded recursion, and a characterization of its complexity and expressive power. Although finite, the resulting class of programs is highly expressive since its data complexity is complete for the elementary functions.

Δ: Set-theoretic query language capturing LOGSPACE

Two versions of a set theoretic Δ-language are considered as theoretical prototypes for database query languages with “nested”, “unstructured” data where database states and queries are represented as hereditarily-finite (HF) sets and set theoretic operations, respectively. It is shown that these versions correspond exactly to (N/D)LOGSPACE computability over HF relative to a special graph representation (encoding) of HF-sets. Such languages over sets, capturing also PTIME, were introduced in previous works, however, descriptions of LOGSPACE over HF [34] were not completely satisfactory. Here we overcome the drawbacks of the previous approaches by some new partial result on definability of a linear ordering over finite extensional acyclic graphs and present a unified and simplified approach.

A spatiotemporal database model and query language

Conventional spatial databases support efficiently a spatial management for objects. However, they manage only those that are valid at current time. Owing to this property, whenever a new value is inserted into databases, the old one should be deleted. So, it is very difficult for time varying spatial information to manage efficient historical information. To solve this problem, there is a rapid increase of interest for spatiotemporal databases. Spatiotemporal databases support historical information as well as spatial management at the same time, so that they can be used in various application areas such as geographic information system, urban plan system, and car navigation system, and so on. In this paper, we suggest a spatiotemporal data model that supports a bitemporal concept for spatial objects, and design a spatiotemporal database query language, entitled as STQL as well. When it is compared with the results of previous researches, it is the first spatiotemporal query language that supports temporal concept and spatial expression as well.

Natural language querying of databases: an information extraction approach in the conceptual query language

Natural language (NL) interfaces for database (DB) query formulation have always been recognized as a much-needed enhancement for DB end-users. NL systems, however, have shortcomings that have led some DB researchers to question their practicality. The drawbacks stem primarily from their weak interpretative power. This weakness is, to a large extent, due to their inability to deal with the nuances in human use of natural language. Some studies, however, show that NL database systems are practical and useful in narrow domains like DB querying. One way of addressing the difficulty with NL database query languages (DBQLs) is to combine concept-based DBQL paradigms with NL approaches to enhance the overall ease-of-use of the query interface. In this study, the conceptual query language-with-natural language (CQL/NL) is proposed. CQL/NL uses information extraction methods to filter NL query statements for search predicates that are derived from constructs on conceptual schemas. In this way, it avoids the computational difficulty with full-fledged NL parsing. In the main, we draw on certain concepts in natural language processing and computational linguistics to develop CQL/NL.

Kaleidoquery—A Flow-based Visual Language and its Evaluation

This paper describes the Kaleidoquery visual query language for object databases and its comparative evaluation with object query language (OQL). The design philosophy behind the filter flow nature of Kaleidoquery and each of the language's constructs is described, and examples are given that allow comparisons to be made with OQL. This is followed by a description of an experiment with the Kaleidoquery and OQL languages. Two groups of subjects, programmers and non-programmers, were taught aspects of OQL and Kaleidoquery, and then tested under experimental conditions. Results show that both groups answered significantly more correct queries using certain constructs of the Kaleidoquery language.

Comparative analysis of five XML query languages

XML is becoming the most relevant new standard for data representation and exchange on the WWW. Novel languages for extracting and restructuring the XML content have been proposed, some in the tradition of database query languages (i.e. SQL, OQL), others more closely inspired by XML. No standard for XML query language has yet been decided, but the discussion is ongoing within the World Wide Web Consortium and within many academic institutions and Internet-related major companies. We present a comparison of five, representative query languages for XML, highlighting their common features and differences.

A query resolution engine to handle a path operator with multiple paths

An end-user query of a Geographical Information System (GIS) can formally be defined as the application of a set of operators (spatial or not). Geographical Information Systems used for Transportation (GIS-T) must provide a path evaluation operator. For example, an end-user query may involve a selection based on alphanumeric criteria, an evaluation of path, and a spatial intersection. This composition of operators and the fact that the evaluation of a path may not provide a unique result impose the definition of a query resolution model or a database query language able to support this composition. In this paper we present a query resolution model. The use of multi-criteria analysis and the definition of aggregates in a query (nearly mandatory) may involve ambiguities in the final presentation of the results to an end-user. The formal modeling of query results must take into account this risk. The philosophies of a query definition and the presentation of the results may be different (e.g., formular vs visual). The management of query results must take into account the data model associated with the query results, the results themselves (metabase/database), and the interpretation. The interpretation avoids errors due to visual ambiguities of an operator with an aggregate function.

Querying XML documents

Web based environments will typically need to maintain many documents (e.g. simulation model information and data results from multiple sites). Ideally, this information would be held in a widely utilized and highly viewable format. The eXtensible Markup Language (XML) is a new standard that meets this criteria for World Wide Web based applications. It is sophisticated enough so that complex real world structures and relationships may be captured. Large collections of XML documents can be stored for efficient retrieval using database management systems (DBMSs). Current database management is represented by the object oriented (OO) and object-relational (OR) database systems. Each type has their own query languages, Object Query Language (OQL, v.2) and Structured Query Language (SQL), respectively. These database query languages provide a high-level way to ask for information from a database. The article looks at storing and retrieving XML documents. It surveys work being done on query languages and tools for XML. It then discusses a simple graphical XML query tool for front end use in the Java Simulation (JSIM) Web based simulation environment.