892182
Operational equivalence for interaction nets
The notion of contextual (or operational) equivalence is fundamental in the theory of programming languages. By setting up a notion of bisimilarity, and showing that it coincides with contextual equivalence, one obtains a simple coinductive proof technique for showing that two programs are equivalent in all contexts. In this paper we apply these (now standard) techniques to interactions nets, a graphical programming language characterized by local reduction. This work generalizes previous studies of operational equivalence in typed interaction nets since it can be applied to untyped systems, thus all systems of interaction nets are captured.
6993516
A Theory of Operational Equivalence for Interaction Nets
The notion of contextual equivalence is fundamental in the theory of programming languages. By setting up a notion of bisimilarity, and showing that it coincides with contextual equivalence, one obtains a simple coinductive proof technique for showing that two programs are equivalent in all contexts. In this paper we apply these (now standard) techniques to interactions nets, a graphical programming language characterized by local reduction. This work generalizes previous studies of operational equivalence in interaction nets since it can be applied to untyped systems, thus all systems of interaction nets are captured.
11746228
Interaction Nets and Term-Rewriting Systems
Abstract Term-rewriting systems provide a framework in which it is possible to specify and program in a traditional syntax (oriented equations). Interaction nets, on the other hand, provide a graphical syntax for the same purpose, but can be regarded as being closer to an implementation since the reduction process is local and asynchronous, and all the operations are made explicit, including discarding and copying of data. Our aim is to bridge the gap between the above formalisms by showing how to understand interaction nets in a term-rewriting framework. This allows us to transfer results from one paradigm to the other, deriving syntactical properties of interaction nets from the (well-studied) properties of term-rewriting systems; in particular concerning termination and modularity.
16649053
Coinductive techniques for operational equivalence of interaction nets
In this paper we study a notion of operational equivalence for interaction nets, following the recent success of applying methods based on bisimulation to functional and object oriented programming languages. We set up notions of contextual equivalence and bisimilarity and show that they coincide. A coinduction principle then gives a simple and robust way of showing when two interaction nets are contextually equivalent. We include several examples to demonstrate the usefulness of the approach, in particular for optimizing interaction nets.
1019046
Implementing Nominal Unification
Nominal matching and unification underly the dynamics of nominal rewriting. Urban, Pitts and Gabbay gave a nominal unification algorithm which finds the most general solution to a nominal matching or unification problem, if one exists. Later the algorithm was extended by Fernandez and Gabbay to deal with name generation and locality. In this paper we describe first a direct implementation of the nominal unification algorithm, including the extensions, in Maude. This implementation is not efficient (it is exponential in time), but we will show that we can obtain a feasible implementation by using termgraphs.
17556593
Type assignment and termination of interaction nets
Interaction nets have proved to be a useful tool for the study of computational aspects of various formalisms (e.g. λ-calculus, term rewriting systems), but they are also a programming paradigm in themselves, and this is actually how they were introduced by Lafont. In this paper we consider semi-simple interaction nets as a programming language, and present a type assignment system using intersection types. First we show that interactions preserve types (i.e., the system enjoys subject reduction), and we compare this type assignment system with the intersection systems for λ-calculus and term rewriting systems. Then we define a recursion scheme that ensures termination of all interaction sequences. By relaxing the scheme and using the type assignment system, we derive another sufficient condition for termination of interaction nets. Finally, we show that although the type system based on general intersection types is not decidable, its restriction to rank 2 types is, and we give an algorithm that computes principal types for nets.
9830270
Declarative specification of Web sites with Strudel
Abstract. Strudel is a system for implementing data-intensive Web sites, which typically integrate information from multiple data sources and have complex structure. Strudel's key idea is separating the management of a Web site's data, the specification of its content and structure, and the visual representation of its pages. Strudel provides a declarative query language for specifying a site's content and structure, and a simple template language for specifying a site's HTML representation. This paper contains a comprehensive description of the Strudel system and details the benefits of declarative site specification. We describe our experiences using Strudel in a production application and describe three different, but complementary, systems that extend and improve upon Strudel's original ideas.
1297751
Storing semistructured data with STORED
Systems for managing and querying semistructured-data sources often store data in proprietary object repositories or in a tagged-text format. We describe a technique that can use relational database management systems to store and manage semistructured data. Our technique relies on a mapping between the semistructured data model and the relational data model, expressed in a query language called STORED. When a semistructured data instance is given, a STORED mapping can be generated automatically using data-mining techniques. We are interested in applying STORED to XML data, which is an instance of semistructured data. We show how a document-type-descriptor (DTD), when present, can be exploited to further improve performance.
14930878
SilkRoute: A framework for publishing relational data in XML
XML is the "lingua franca" for data exchange between interenterprise applications. In this work, we describe SilkRoute, a framework for publishing relational data in XML. In SilkRoute, relational data is published in three steps: the relational tables are presented to the database administrator in a canonical XML view; the database administrator defines in the XQuery query language a public, virtual XML view over the canonical XML view; and an application formulates an XQuery query over the public view. SilkRoute composes the application query with the public-view query, translates the result into SQL, executes this on the relational engine, and assembles the resulting tuple streams into an XML document. This work makes some key contributions to XML query processing. First, it describes an algorithm that translates an XQuery expression into SQL. The translation depends on a query representation that separates the structure of the output XML document from the computation that produces the document's content. The second contribution addresses the optimization problem of how to decompose an XML view over a relational database into an optimal set of SQL queries. We define formally the optimization problem, describe the search space, and propose a greedy, cost-based optimization algorithm, which obtains its cost estimates from the relational engine. Experiments confirm that the algorithm produces queries that are nearly optimal.
14181773
Nominal rewriting
Nominal rewriting is based on the observation that if we add support for @a-equivalence to first-order syntax using the nominal-set approach, then systems with binding, including higher-order reduction schemes such as @l-calculus beta-reduction, can be smoothly represented. Nominal rewriting maintains a strict distinction between variables of the object-language (atoms) and of the meta-language (variables or unknowns). Atoms may be bound by a special abstraction operation, but variables cannot be bound, giving the framework a pronounced first-order character, since substitution of terms for variables is not capture-avoiding. We show how good properties of first-order rewriting survive the extension, by giving an efficient rewriting algorithm, a critical pair lemma, and a confluence theorem for orthogonal systems.
3338932
Querying XML Data
XML threatens to expand beyond its document markup origins to become the basis for data interchange on the Internet. One highly anticipated application of XML is the interchange of electronic data (EDI). Unlike existing Web documents, electronic data is primarily intended for computer, not human, consumption. For example, businesses could publish data about their products and services, and potential customers could compare and process this information automatically; business partners could exchange internal operational data between their information systems on secure channels; search robots could integrate automatically information from related sources that publish their data in XML format, like stock quotes from financial sites, sports scores from news sites. New opportunities will arise for third parties to add value by integrating, transforming, cleaning, and aggregating XML data. Once it becomes pervasive, it’s not hard to imagine that many information sources will structure their external view as a repository of XML data, no matter what their internal storage mechanisms. Data exchange between applications will then be in XML format. What is then the role of a query language in this world? One could see it as a local adjunct to a browsing capability, providing a more expressive “find” command over one or more retrieved documents. Or it might serve as a souped-up version of XPointer, allowing richer forms of logical reference to portions of documents. Neither of these modes of use is very “databasey”. From the database viewpoint, the enticing role of an XML query language is as a tool for structural and content-based query that allows an application to extract precisely the information it needs from one or several XML data sources. One salient question is why not adapt SQL or OQL to query XML. The answer is that XML data is fundamentally different from relational and object-oriented data, and therefore, neither SQL nor OQL is appropriate for XML. The key distinction between data in XML and data in traditional models is that XML is not rigidly structured. In the relational and object-oriented models, every data instance has a schema, which is separate from and independent of the data. In XML, the schema exists with the data. Thus, XML data is self-describing and can naturally model irregularities that cannot be modeled by relational or object-oriented data. For example, data items may have missing elements or multiple occurrences of the same element; elements may have atomic values in some data items and structured values in others; and collections of elements can have heterogeneous structure. Even XML data that has an associated DTD is self-describing (the data can still be parsed, even if