We demonstrate the Search Computing framework for multi-domain queries upon ranked data collected from Web sources. Search Computing answers to queries like "Find a good Jazz concert close to a specified location, a good restaurant and a hotel at walking distance" and fills the gap between generic and domain-specific search engines, by proposing new methods, techniques, interfaces, and tools for building search-based applications spanning multiple data services. The main enabling technology is an execution engine supporting methods for rank-join execution upon ranked data sources, abstracted and wrapped by means of a unifying service model. The demo walks through the interface for formulating multi-domain queries and follows the steps of the query engine that builds the result, with the help of run-time monitors that clearly explain the system's behavior. Once results are extracted, the demonstration shows several approaches for visualizing results and exploring the information space.

Continuous SPARQL (C-SPARQL) is proposed as new language for continuous queries over streams of RDF data. It covers a gap in the Semantic Web abstractions which is needed for many emerging applications, including our focus on Urban Computing. In this domain, sensor-based information on roads must be processed to deduce localized traffic conditions and then produce traffic management strategies. Executing C-SPARQL queries requires the effective integration of SPARQL and streaming technologies, which capitalize over a decade of research and development; such integration poses several nontrivial challenges.

C-SPARQL is an extension of SPARQL to support continuous queries, registered and continuously executed over RDF data streams, considering windows of such streams. Supporting streams in RDF format guarantees interoperability and opens up important applications, in which reasoners can deal with knowledge that evolves over time. We present C-SPARQL by means of examples in Urban Computing.

Many data integration solutions in the market today include tools for schema mapping, to help users visually relate elements of different schemas. Schema elements are connected with lines, which are interpreted as mappings, i.e. high-level logical expressions capturing the relationship between source and target data-sets; these are compiled into queries and programs that convert source-side data instances into target-side instances. This paper describes Clip, an XML schema mapping tool distinguished from existing tools in that mappings explicitly specify structural transformations in addition to value couplings. Since clip maps hierarchical XML schemas, lines appear naturally nested. We describe the transformation semantics associated with our "lines" and how they combine to form mappings that are more expressive than those generated by Clio, a well-known mapping tool. Further, we extend Clio's mapping generation algorithms to generate Clip's mappings.

Many data integration solutions in the market today include visual tools for schema mapping. Users connect schema elements with lines that are interpreted as high-level logical expressions capturing the relationship between source and target data-sets. These expressions are compiled into queries or programs that convert source-side data instances into target-side instances. In this demo we showcase Clip, an XML Schema mapping tool. Clip is distinguished from existing tools in that mappings explicitly specify structural transformations in addition to value correspondences. We show how Clip's users enter mappings by drawing lines and how these lines are translated into XQuery.

Where can I attend an interesting database workshop close to a sunny beach? Who are the strongest experts on service computing based upon their recent publication record and accepted European projects? Can I spend an April weekend in a city served by a low-cost direct flight from Milano offering a Mahler's symphony? We regard the above queries as multi-domain queries, i.e., queries that can be answered by combining knowledge from two or more domains (such as: seaside locations, flights, publications, accepted projects, conference offerings, and so on). This information is available on the Web, but no general-purpose software system can accept the above queries nor compute the answer. At the most, dedicated systems support specific multi-domain compositions (e.g., Google-local locates information such as restaurants and hotels upon geographic maps). This paper presents an overall framework for multi-domain queries on the Web. We address the following problems: (a) expressing multi-domain queries with an abstract formalism, (b) separating the treatment of "search" services within the model, by highlighting their differences from "exact" Web services, (c) explaining how the same query can be mapped to multiple "query plans", i.e., a well-defined scheduling of service invocations, possibly in parallel, which complies with their access limitations and preserves the ranking order in which search services return results; (d) introducing cross-domain joins as first-class operation within plans; (e) evaluating the query plans against several cost metrics so as to choose the most promising one for execution. This framework adapts to a variety of application contexts, ranging from end-user-oriented mash-up scenarios up to complex application integration scenarios.

XQBE (XQuery By Example) is a visual XML query language which, coherently with the hierarchical XML data model, uses tree-shaped structures to express queries and transformations over XML documents. These structures are annotated to express selection predicates; explicit bindings between the nodes of such structures visualize the input/output mappings.XQuery and XSLT, the standard query and transformation languages for XML, happen to be too complex for most occasional or unskilled users who might need to specify queries, schema mappings, or document transformations, if they are only aware of the basics of the XML data model. The implementation of XQBE allows to generate the XQuery and XSLT translations of the visual queries, assisting the user in several aspects of the interaction (e.g. providing interactive access to schema information); therefore, XQBE provides an integrated environment where users can edit the visual queries and their textual counterparts, executing them on several engines. Alternating among different representations of the same query is valuable for training beginners, as we have experienced in our database courses.

The spreading of XML data in many contexts of modern computing infrastructures and systems causes a pressing need for adequate XML querying capabilities; to address this need, the W3C is proposing XQuery as the standard query language for XML, with a language paradigm and a syntactic flavor comparable to the SQL relational language. XQuery is designed for meeting the requirements of skilled database programmers; its inherent complexity makes the new language unsuited to unskilled users.In this article we present XQBE (XQuery By Example), a visual query language for expressing a large subset of XQuery in a visual form. In designing XQBE, we targeted both unskilled users and expert users wishing to speed up the construction of their queries; we have been inspired by QBE, a relational language initially proposed as an alternative to SQL, which is supported by Microsoft Access. QBE is extremely successful among users who are not computer professionals and do not understand the subtleties of query languages, as well as among professionals who can draft their queries very quickly.According to the hierarchical nature of XML, XQBE's main graphical elements are trees. One or more trees denote the documents assumed as query input, and one tree denotes the document produced by the query. Similar to QBE, trees are annotated so as to express selection predicates, joins, and the passing of information from the input trees to the output tree.This article formally defines the syntax and semantics of XQBE, provides a large set of examples, and presents a prototype implementation.

XQuery, the standard query language for XML, is increasingly popular among computer scientists with a SQL background, since queries in XQuery and SQL require comparable skills to be formulated. However, the number of these experts is limited, and the availability of easier XQuery "dialects" could be extremely valuable. With this motivation in mind, we designed XQBE, a dialect of XQuery inspired by the QBE language (query by example). QBE, initially proposed as an alternative to SQL, has then become popular as the user-friendly query language supported by MS Access. XQBE starts from hierarchical structures, coherent with the hierarchical nature of XML, and uses one or more structures to denote the input documents, and one structure to denote the XML document produced in output. These structures are annotated to express selection predicates; explicit bindings connecting the nodes of these structures visualize the input/output mappings.

Besides being adopted as the new interchange format for the Internet, XML is finding increasing acceptance as a native data repository language. In order to make XML repositories fully equipped with data management capabilities, suitable query and update languages are being developed. However, once the user is allowed to perform updates, it is perceivably necessary to guarantee the correctness of his/her updates, especially if document validity or semantic constraints are violated. We address this problem by exploiting the well-grounded concept of active rules. In this paper, we propose Active XQuery, an active language for XML repositories that is based on a previously defined XQuery update model. In particular, we present the syntax and semantics of our language, aiming at emulating the trigger definition and execution model of SQL3. An active extension of XQuery results in nontrivial problems, related to the need of interleaving updates and triggers. These problems have led us to define an algorithm for update reformulation and to devise a compact semantics. In conclusion, the paper presents an architecture for rapid prototyping, and considers optimization and research issues.

The recent success of XML as a standard to represent semi-structured data, and the increasing amount of available XML data pose new challenges to the data mining community. In this paper we present the XMINE operator, a tool developed to extract XML association rules for XML documents. The operator, based on XPath and inspired by the syntax of XQuery, allows us to express complex mining tasks, compactly and intuitively. XMINE can be used to specify indifferently (and simultaneously) mining tasks both on the content and on the structure of the data, since the distinction in XML is slight.