Irena Mlýnková

Evolution and change management of XML-based systems

XML is de-facto a standard language for data exchange. Structure of XML documents exchanged among different components of a system (e.g. services in a Service-Oriented Architecture) is usually described with XML schemas. It is a common practice that there is not only one but a whole family of XML schemas each applied in a particular logical execution part of the system. In such systems, the design and later maintenance of the XML schemas is not a simple task. In this paper we aim at a part of this problem - evolution of the family of the XML schemas. A single change in user requirements or surrounding environment of the system may influence more XML schemas in the family. A designer needs to identify the XML schemas affected by a change and ensure that they are evolved coherently with each other to meet the new requirement. Doing this manually is very time consuming and error prone. In this paper we show that much of the manual work can be automated. For this, we introduce a technique based on the principles of Model-Driven Development. A designer is required to make a change only once in a conceptual schema of the problem domain and our technique ensures semi-automatic coherent propagation to all affected XML schemas (and vice versa). We provide a formal model of possible evolution changes and their propagation mechanism. We also evaluate the approach on a real-world evolution scenario.

Even an ant can create an XSD

The XML has undoubtedly become a standard for data representation and manipulation. But most of XML documents are still created without the respective description of its structure, i.e. an XML schema. Hence, in this paper we focus on the problem of automatic inferring of an XML schema for a given sample set of XML documents. In particular, we focus on new features of XML Schema language and we propose an algorithm which is an improvement of a combination of verified approaches that is, at the same time, enough general and can be further enhanced. Using a set of experiments we illustrate the behavior of the algorithm on both real-world and artificial XML data.

XML data transformations as schema evolves

One of the key characteristics of XML applications is their dynamic nature. When a system grows and evolves, old user requirements change and/or new requirements accumulate. Apart from changes in the interface, it is also necessary to modify the existing documents with each new version, so they are valid against the new specification. The approach presented in this paper extends an existing XML conceptual model with the support for multiple versions of the model. Thanks to this extension, it is possible to define a set of changes between two versions of a schema. This work contains an outline of an algorithm that compares two versions of a schema and produces a revalidation script in XSL.

Efficient querying of distributed linked data

The contemporary Web is formed mainly by documents, from which it is rather complicated to automatically retrieve hidden structured and interlinked information. The idea of Linked Data based primarily on RDF data triples seems to successfully follow this drawback. In recent years, a significant effort was made not only in a theoretical research, but also in the amount of Linked Data globally available. Since RDF triples are modelled as graph data, we cannot directly adopt the existing solutions from relational databases or XML technologies. Thus, several research questions remain opened. The purpose of our ongoing research effort is to propose an efficient framework for querying Linked Data. This requires finding the compromise between storing data in local storages and accessing them directly on-demand in distributed data sources. Next, we need to choose a suitable querying language, propose auxiliary indexing structures and, finally, to define an ordering model for query results. The theoretical research will be supplemented by a prototype implementation and experiments over real-world data.

Experimental Comparison of Graph Databases

In the recent years a new type of NoSQL databases, called graph databases (GDBs), has gained significant popularity due to the increasing need of processing and storing data in the form of a graph. The objective of this paper is a research on possibilities and limitations of GDBs and conducting an experimental comparison of selected GDB implementations. For this purpose the requirements of a universal GDB benchmark have been formulated and an extensible benchmarking tool, called BlueBench, has been developed.

When conceptual model meets grammar: a formal approach to semi-structured data modeling

Currently, XML is a standard for information exchange. An important task in XML management is designing particular XML formats suitable for particular kinds of information exchange. There exist two kinds of approaches to this problem. Firstly, there exist XML schema languages and their formalization - regular tree grammars. Secondly, there are approaches based on conceptual modeling and automatic derivation of an XML schema from a conceptual schema. In this paper, we provide a unified formalism for both kind of approaches. It is based on formal specification of XML schemas, conceptual schemas, and mappings between both kinds of schemas. The formalism gives necessary conditions on the mappings. The mapping may then be applied in practice not only for unified process of designing XML schemas on both levels, i.e. conceptual and grammatical, but also for integration and evolution of XML schemas.

Correction of Invalid XML Documents with Respect to Single Type Tree Grammars

XML documents and related technologies represent a widely accepted standard for managing semi-structured data. However, a surprisingly high number of XML documents is affected by well-formedness errors, structural invalidity or data inconsistencies. The aim of this paper is the proposal of a correction framework involving structural repairs of elements with respect to single type tree grammars. Via the inspection of the state space of a finite automaton recognising regular expressions, we are always able to find all minimal repairs against a defined cost function. These repairs are compactly represented by shortest paths in recursively nested multigraphs, which can be translated to particular sequences of edit operations altering XML trees. We have proposed an efficient algorithm and provided a prototype implementation.

Linked data indexing methods: a survey

Documents on the contemporary Web are based especially on HTML formats and, therefore, it is rather difficult to retrieve hidden structured information from them using automated agents. The concept of Linked Data based primarily on RDF data triples seems to successfully solve this drawback. However, we cannot directly adopt the existing solutions from relational databases or XML technologies, because RDF triples are modelled as graph data and not relational or tree data. Despite the research effort in recent years, several questions in the area of Linked Data indexing and querying remain open, not only since the amount of Linked Data globally available significantly increases each year. This paper attempts to introduce advantages and disadvantages of the state-of-the-art solutions and discuss several issues related to our ongoing research effort - the proposal of an efficient querying framework over Linked Data. In particular, our goal is to focus on large amounts of distributed and highly dynamic data.

Towards topic-based trust in social networks

The vast majority of applications consider generic notion of trust of a person to others, which is not restricted to any particular context or situation. Motivated by the financial scenario consuming data from distributed sources on the Web, we argue that we (as information consumers) cannot trust the information publishers or authors in general, however, only regarding the particular topics of the consumed data sources. To enable the so-called topic-based trust between users, we (1) propose a mechanism to persist the topic-based trust in a FOAF social network, (2) survey the topic hierarchies suitable for classifying the topics used in the trust model, and (3) propose an algorithm to compute trust with respect to the particular topic.

Discovering XML keys and foreign keys in queries

The XML has undoubtedly become a standard for data representation and manipulation. But most of XML documents are still created without the respective description of their structure, i.e. an XML schema. In this paper, we further enhance current methods for automatic inferring of an XML schema with discovering keys and foreign keys. We do not consider sample XML data for discovery but a set of queries in XQuery and we show how constructs utilized in the queries can be used for the discovery.