Martin Kempa

A Selective Key-Oriented XML Index for the Index Selection Problem in XDBMS

In relational database management systems indexes are used to accelerate specific queries. The selection of indexes is an important task when tuning a database which is performed by a database administrator or an index propagation tool which suggests a set of suitable indexes. In this paper we introduce a new index approach, called key-oriented XML index (KeyX), that uses specific XML element or attribute values as keys referencing arbitrary nodes in the XML data. KeyX is selective to specific queries avoiding efforts spent for elements which are never queried. This concept reduces memory consumption and unproductive index updates.

Autonomous Index Optimization in XML Databases

Defining suitable indexes is a major task when optimizing a database. Usually, a human database administrator defines a set of indexes in the design phase of the database. This can be done manually or with the help of so called index wizard tools analyzing predefined database operations. Even having an optimal initial set of indexes when setting up a database, there is no guarantee that these indexes will suit future demands. Rather, it is realistic that the typical usage of the database will change after a while because new queries appear, for instance. In consequence, the existing indexes are suboptimal. The typical way to handle this problem is that a database administrator maintains the database permanently. In XML database management systems (XDBMS) this problem becomes even worse: Because XML queries cover both content and structure the number of possible queries and indexes is significantly higher. Additionally, for XML data without schema information, queries and indexes cannot be defined in advance, because the structure and the content of the data is not restricted. Both facts tend to result in higher maintenance costs for XML indexes compared to relational indexes. In this paper we show by performance measurements that an adaptive XDBMS that analyzes its workload periodically and creates/drops XML indexes automatically guarantees a high performance over the total life time of a database. Although we present our index system called KeyX the idea and the results are transferable to other XML indexing approaches.

Model Driven Architecture

Bei der Model Driven Architecture (MDA) bilden Modelle die zentralen Elemente des Softwareentwicklungsprozesses. Ziel ist es, plattformspezifische Modelle möglichst automatisiert aus plattformunabhängigen Modellen abzuleiten. Dadurch soll der Aufwand der Softwareentwicklung verringert und die Adaptierung an neue Technologien erleichtert werden.

XML-Based Applications Using XML Schema

XML Schemas provide a generalization of Document Type Definitions for describing the validity of a set of XML documents. There is a growing number of applications that deal with XML documents in various respects. One area of programs is concerned with analyzing XML documents arriving, for example, over the internet. Another rapidly expanding area is best described by the term XML generators. XML generators usually are part of a WWW system, for example generators for XML documents serving as views of data bases. Although XML Schemas provide a concise means for describing the syntax of correct XML documents in a specific domain, XML generators usually treat the XML documents as unstructured strings or, in the context of the Document Object Model, as trees the nodes of which belong to an unspecific Element-interface. The syntactical correctness, i.e. the validity of the generated XML documents cannot be guaranteed at compile time but must be tested at runtime. This means that, in general, there is no ultimate proof that an XML generator generates only valid documents according to an underlying XML schema. This paper addresses this problem by introducing a new distinct interface for each element defined within an XML schema. Each interface extends the Element-interface of the Document Object Model. This mechanism provides a generalization of a previous approach based on the weaker concept of Document Type Definitions presented by the authors.

V-DOM and P-XML—towards a valid programming of XML-based applications

Abstract Many WWW applications generate hypertext markup language or extensible markup language (XML) documents dynamically. Current tools, however, like languages using document object model (DOM) or JAVA Server Pages do not allow to check the validity of the generated documents statically. Instead, validity has to be ‘checked’ dynamically by appropriate test runs. This paper addresses this problem by introducing a new distinct class for each element type of a document type definition (DTD). Each class extends the Element -class of the DOM. The resulting object model is called validating DOM (V-DOM). Parametric XML (P-XML) is an extension of XML allowing to insert values of the newly defined classes in places, where the corresponding element types are allowed according to the underlying DTD. Like V-DOM, P-XML guarantees the validity of all XML documents generated by using P-XML. V-DOM and P-XML are illustrated by several examples.

Sprachen und Werkzeuge zur Generierung von HTML- und XML-Dokumenten

Inhalte von Webseiten werden heute zu einem großen Teil beispielsweise mit Hilfe des Inhalts von Datenbanken oder aus aktuellen Daten wie Aktienkursen oder Wetterdaten dynamisch generiert. Es gibt eine Fülle von Sprachen für die Realisierung solcher Webanwendungen.Summary. Nowadays, contents of web pages are very often generated dynamically, for example by integrating the results of data base queries or by using up to date stock exchange data or weather data. Numerous languages exist for implementing these web applications. In this paper, some languages are considered which, at least in part, are concerned with the generation of HTML- or XML-Documents. It is shown that, besides being rather complicated, these languages allow to ”prove” the validity of the generated structures only at runtime. A proposal which is currently being developed in Lübeck allows to check the validity of the generated HTML- and XML-documents at compile time.