12 research outputs found
Logics for Unranked Trees: An Overview
Labeled unranked trees are used as a model of XML documents, and logical
languages for them have been studied actively over the past several years. Such
logics have different purposes: some are better suited for extracting data,
some for expressing navigational properties, and some make it easy to relate
complex properties of trees to the existence of tree automata for those
properties. Furthermore, logics differ significantly in their model-checking
properties, their automata models, and their behavior on ordered and unordered
trees. In this paper we present a survey of logics for unranked trees
Escape from Winchester Mansion – Toward a Set of Design Principles to Master Complexity in IT Architectures
Although the management of complexity is a central task of CIOs and IT architects, in-depth examinations and the development of design theory in this area is, to the best of our knowledge, underrepresented in existing IS literature. Especially theory-based guidelines and information systems for the management of IT architecture complexity are missing. In a joint team of practitioners and researchers, we applied the action design research (ADR) method in order to tackle this class of problems, i.e., IT architecture complexity management. We derived a set of seven design principles (that guide the design of an information system that supports IT architects to manage IT architecture complexity), which we evaluated and enriched during multiple ‘building, intervention and evaluation’ cycles, according to ADR. In addition, we simultaneously implemented and evaluated a material artifact (i.e., a piece of software) for IT architecture complexity management
Automatic structures of bounded degree revisited
The first-order theory of a string automatic structure is known to be
decidable, but there are examples of string automatic structures with
nonelementary first-order theories. We prove that the first-order theory of a
string automatic structure of bounded degree is decidable in doubly exponential
space (for injective automatic presentations, this holds even uniformly). This
result is shown to be optimal since we also present a string automatic
structure of bounded degree whose first-order theory is hard for 2EXPSPACE. We
prove similar results also for tree automatic structures. These findings close
the gaps left open in a previous paper of the second author by improving both,
the lower and the upper bounds.Comment: 26 page
Definable relations and first-order query languages over strings
International audienceWe study analogs of classical relational calculus in the context of strings. We start by studying string logics. Taking a classical model-theoretic approach, we fix a set of string operations and look at the resulting collection of definable relations. These form an algebra-a class of n-ary relations for every n, closed under projection and Boolean operations. We show that by choosing the string vocabulary carefully, we get string logics that have desirable properties: computable evaluation and normal forms. We identify five distinct models and study the differences in their model-theory and complexity of evaluation. We identify a subset of these models which have additional attractive properties, such as finite VC dimension and quantifier elimination. Once you have a logic, the addition of free predicate symbols gives you a string query language. The resulting languages have attractive closure properties from a database point of view: while SQL does not allow the full composition of string pattern-matching expressions with relational operators, these logics yield compositional query languages that can capture common string-matching queries while remaining tractable. For each of the logics studied in the first part of the paper, we study properties of the corresponding query languages. We give bounds on the data complexity of queries, extend the normal form results from logics to queries, and show that the languages have corresponding algebras expressing safe queries
Definable Relations and First-Order Query Languages over Strings
We study analogs of classical relational calculus in the context of strings. We start by studying string logics