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Architectural aspects of architectural aspects

This document studies in some detail the recently developed concept of aspect at the architecture level. This concept introduces a novel kind of modularization and composition in software, and therefore it defines new structures which must be studied by Software Architecture, determining the architectural features of aspects. However the opposite strategy can also be considered; namely, a new conceptual model can be defined, including an architecture-level notion of aspect. This would provide a new abstraction to describe software structures, thus effectively providing an additional dimension in architecture description, and would enable the study of the specific compositional problems in this dimension. The document starts by addressing the relevance of this kind of study, and continues by discussing why the new notions are necessary. Then it continues by including a brief enumeration of the more relevant notions derived from this aspectual framework, with particular emphasis on their relationship with software components. Next the document explores the different forms in which these notions could be incorporated into the context of Software Architecture, revealing a rather extensive variety of approaches, and also the relationships and partial equivalences between them.The paper concludes by noting a number or open questions and futures areas of research within this context.

UML Automatic Verification Tool with Formal Methods

The use of the UML specification language is very widespread due to some of its features. However, the ever more complex systems of today require modeling methods that allow errors to be detected in the initial phases of development. The use of formal methods make such error detection possible but the learning cost is high.This paper presents a tool which avoids this learning cost, enabling the active behavior of a system expressed in UML to be verified in a completely automatic way by means of formal method techniques. It incorporates an assistant for the verification that acts as a user guide for writing properties so that she/he needs no knowledge of either temporal logic or the form of the specification obtained.

A graphical user interface for the retrieval of hierarchically structured documents

Past research has proved that graphical user interfaces (GUIs) can significantly improve the effectiveness of the information access task. Our work is based on the consideration that structured document retrieval requires different user graphical interfaces from standard information retrieval. In structured document retrieval a GUI has to enable a user to query, browse retrieved documents, provide query refinement and relevance feedback based not only on full documents, but also on specific document parts in relation to the document structure. In this paper, we present a new GUI for structured document retrieval specifically designed for hierarchically structured documents. A user task-oriented evaluation has shown that the proposed interface provides the user with an intuitive and powerful set of tools for structured document searching, retrieved list navigation, and search refinement.

Using structural contexts to compress semistructured text collections

We describe a compression model for semistructured documents, called Structural Contexts Model (SCM), which takes advantage of the context information usually implicit in the structure of the text. The idea is to use a separate model to compress the text that lies inside each different structure type (e.g., different XML tag). The intuition behind SCM is that the distribution of all the texts that belong to a given structure type should be similar, and different from that of other structure types. We mainly focus on semistatic models, and test our idea using a word-based Huffman method. This is the standard for compressing large natural language text databases, because random access, partial decompression, and direct search of the compressed collection is possible. This variant, dubbed SCMHuff, retains those features and improves Huffmans compression ratios. We consider the possibility that storing separate models may not pay off if the distribution of different structure types is not different enough, and present a heuristic to merge models with the aim of minimizing the total size of the compressed database. This gives an additional improvement over the plain technique. The comparison against existing prototypes shows that, among the methods that permit random access to the collection, SCMHuff achieves the best compression ratios, 2-4% better than the closest alternative. From a purely compression-aimed perspective, we combine SCM with PPM modeling. A separate PPM model is used to compress the text that lies inside each different structure type. The result, SCMPPM, does not permit random access nor direct search in the compressed text, but it gives 2-5% better compression ratios than other techniques for texts longer than 5MB.

Context representation for web search results

Context has long been considered very useful to help the user assess the actual relevance of a document. In web searching, context can help assess the relevance of a web page by showing how the page is related to other pages in the same web site, for example. Such information is very difficult to convey and visualize in a user friendly way. In this paper we present the design, implementation and evaluation of a graphical visualization tool aimed at helping users to determine the relevance of a web page by displaying the structure of the web site the page belongs to. The results of an initial evaluation suggest that this visualization technique helps the user navigate large web sites and find useful information in an effective way, without increasing the cognitive load of the user.

Lempel‐Ziv compression of highly structured documents

The authors describe Lempel-Ziv to Compress Structure (LZCS), a novel Lempel-Ziv approach suitable for compressing structured documents. LZCS takes advantage of repeated substructures that may appear in the documents, by replacing them with a backward reference to their previous occurrence. The result of the LZCS transformation is still a valid structured document, which is human-readable and can be transmitted by ASCII channels. Moreover, LZCS transformed documents are easy to search, display, access at random, and navigate. In a second stage, the transformed documents can be further compressed using any semistatic technique, so that it is still possible to do all those operations efficiently; or with any adaptive technique to boost compression. LZCS is especially efficient in the compression of collections of highly structured data, such as extensible markup language (XML) forms, invoices, e-commerce, and Web-service exchange documents. The comparison with other structure-aware and standard compressors shows that LZCS is a competitive choice for these type of documents, whereas the others are not well-suited to support navigation or random access. When joined to an adaptive compressor, LZCS obtains by far the best compression ratios.

Reflection-Based, Aspect-Oriented Software Architecture

The Software Architecture discipline is devoted to the study and description of structures, created by the composition of software modules. At the same time, the most important merit of Aspect Orientation is the fact that it introduces a new kind of modularization, deployed in a range of new dimensions, orthogonally to traditional models. These fields are able not only to combine, but also to complement and extend each other. They show also remarkable coincidences in some of their key concepts, such as multiple viewpoints and connectors. This paper explores their relationship, in particular from the point of view of the specification of “aspect-oriented architectures” in terms of existing Architecture Description Languages (Adls). Specifically, we consider the language \(\mathcal {PIL}\)ar: a reflective, process-algebraic Adl conceived for the description of dynamic architectures. It has three conceptual foundations which have also been proposed as a basis for aspect-orientation, namely reflection, superimposition and process algebras. We show how, due to the semantics of its reification relationship, \(\mathcal {PIL}\)ar is capable to directly describe “architectural aspects” with no need for syntactic extensions. At the same time, we suggest that the addition of these extensions could be very useful anyway. The discussion is supported by an example of a coordination aspect in \(\mathcal {PIL}\)ar, based on the classical Paxos Consensus algorithm.

Coordination in a Reflective Architecture Description Language

Software Architecture studies the structure of software systems, as described by Architecture Description Languages (Adls). When these capture structures of change, they are comparable to Coordination Languages. Previous work suggests that the combination with Reflection concepts renders a general framework for the description of such evolving structures. This paper describes a reflective Adl named PiLar designed to provide such a framework. It consists of a structural part, which describes the static skeleton, and a dynamic part, which defines patterns of change. The major novelty is the reification relationship, which structures a description in several meta-layers, such that the architecture is able to reason and act upon itself. The paper includes a complete PiLar example, to show the languages use and some of its most relevant features. It describes a Tuple Space model, illustrating the analogy with existing Coordination Models. We conclude by emphasizing PiLars generality and applicability.

Introducing Reflection in Architecture Description Languages

This document describes the structure of PiLar, an Architectural Description Language based on concepts from the field of Reflection, following a proposal suggested in previous work. First, motivations and ideas behind its design are outlined. Next, the language is divided in two parts: a declarative Structural Language, which makes possible to define an architecture’s static skeleton; and an imperative Dynamic Language, which appears as a set of constraining rules written in a concurrent language. Both languages are intertwined with the reification concept, which has a reflective origin. Its meaning and consequences are commented in detail. After this, the language’s formal semantics are informally described; it is conceived as a system of concurrent processes, communicating by means of channels. It is argued that this semantics fits perfectly with architectural concepts. Finally, a solution for the classical problem of the Dining Philosophers is included as an example, to show how this Adl describes the dynamic evolution in a system. The paper concludes emphasizing the generality and usefulness of the language.

A Graphical User Interface for Structured Document Retrieval

Structured document retrieval requires different user graphical interfaces from standard Information Retrieval. An Information Retrieval system dealing with structured documents has to enable a user to query, browse retrieved documents, provide query refinement and relevance feedback based not only on full documents, but also on specific document structural parts. In this paper, we present a new graphical user interface for structured document retrieval that provides the user with an intuitive and powerful set of tools for structured document searching, retrieved list navigation, and search refinement. We also present the results of a preliminary evaluation of the interface which highlights strengths and weaknesses of the current implementation and suggests directions of future work.