Davidson, Susan B

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  • Publication
    Communicating Shared Resources: A Paradigm for Integrating Real-Time Specification and Implementation
    (1991-03-15) Lee, Insup; Davidson, Susan B; Gerber, Richard
    The timed behavior of distributed real-time systems can be specified using a formalism called Communicating Shared Resources, or CSR. The underlying computation model of CSR is resource-based in which multiple resources execute synchronously, while processes assigned to the same resource are interleaved according to their priorities. CSR bridges the gap between an abstract computation model and implementation environments, but is too complex to be treated as a process algebra. We therefore give a calculus for CSR (CCSR), that provides the ability to perform equivalence proofs by syntactic manipulation. We illustrate how a CSR specification can be translated into the CCSR formalism using a periodic timed producer-consumer example, and how a translated CSR specification can be shown correct using syntactic manipulations.
  • Publication
    ViteX : a Streaming XPath Processing System
    (2005-04-01) Chen, Yi; Davidson, Susan B.; Zheng, Yifeng
    We present ViteX, an XPath processing system on XML streams with polynomial time complexity. ViteX uses a polynomial-space data structure to encode an exponential number of pattern matches (in the query size) which are required to process queries correctly during a single sequential scan of XML. Then ViteX computes query solutions by probing the data structure in a lazy fashion without enumerating pattern matches.
  • Publication
    A Bi-Labeling Based XPath Processing System
    (2010-01-01) Chen, Yi; Davidson, Susan B; Zheng, Yifei
    We present BLAS, a Bi-LAbeling based XPath processing System. BLAS uses two labeling schemes to speed up query processing: P-labeling for processing consecutive child (or parent) axis traversals, and D-labeling for processing descendant (or ancestor) axis traversals. XML data are stored in labeled form and indexed. Algorithms are presented for translating XPath queries to SQL expressions. BLAS reduces the number of joins in the SQL query translated from a given XPath query and reduces the number of disk accesses required to execute the SQL query compared with the traditional XPath processing using D-labeling alone. We also propose an approximate P-labeling scheme and the corresponding query translation algorithm to handle XML data trees that contain a large number of distinct tag names, and/or are very deep. This extension captures a spectrum of XPath-to-SQL query translation schemes, ranging from existing schemes that do not use P-labels to the one that uses exact P-labels. Experimental results demonstrate the efficiency of the BLAS system.
  • Publication
    Reasoning about Keys for XML
    (2001-09-08) Buneman, Peter; Davidson, Susan B.; Fan, Wenfei; Hara, Carmem; Tan, Wang-Chiew
    We study absolute and relative keys for XML, and investigate their associated decision problems. We argue that these keys are important to many forms of hierarchically structured data including XML documents. In contrast to other proposals of keys for XML, these keys can be reasoned about efficiently. We show that the (finite) satisfiability problem for these keys is trivial, and their (finite) implication problem is finitely axiomatizable and decidable in PTIME in the size of keys.
  • Publication
    Indexing Keys in Hierarchical Data
    (2001-01-01) Chen, Yi; Davidson, Susan B.; Zheng, Yifeng
    Building on a notion of keys for XML, we propose a novel indexing scheme for hierarchical data that is based not only on the structure but also the content of the data. The index can be used to check the validity of data with respect to a set of key specifications, as well as for efficiently evaluating queries and updates on key paths. We develop algorithms for the construction and incremental maintenance of the indexing structure, and study the complexity of these algorithms. Finally, we discuss how our indexing techniques can be used for more general queries involving key paths.
  • Publication
    Labeling Recursive Workflow Executions On-the-Fly
    (2011-06-01) Bao, Zhuowei; Davidson, Susan B.; Milo, Tova
    This paper presents a compact labeling scheme for answering reachability queries over workflow executions. In contrast to previous work, our scheme allows nodes (processes and data) in the execution graph to be labeled on-the-fly, i.e., in a dynamic fashion. In this way, reachability queries can be answered as soon as the relevant data is produced. We first show that, in general, for workflows that contain recursion, dynamic labeling of executions requires long (linear-size) labels. Fortunately, most real-life scientific workflows are linear recursive, and for this natural class we show that dynamic, yet compact (logarithmic-size) labeling is possible. Moreover, our scheme labels the executions in linear time, and answers any reachability query in constant time. We also show that linear recursive workflows are, in some sense, the largest class of workflows that allow compact, dynamic labeling schemes. Interestingly, the empirical evaluation, performed over both real and synthetic workflows, shows that our proposed dynamic scheme outperforms the state-of-the-art static scheme for large executions, and creates labels that are shorter by a factor of almost 3.
  • Publication
    Using XQuery to Build Updatable XML Views Over Relational Databases
    (2003-01-01) Braganholo, Vanessa P; Davidson, Susan B.; Heuser, Carlos A
    XML has become an important medium for data exchange, and is frequently used as an interface to - i.e. a view of - a relational database. Although much attention has been paid to the problem of querying relational databases through XML views, the problem of updating relational databases through XML views has not been addressed. In this paper we investigate how a subset of XQuery can be used to build updatable XML views, so that an update to the view can be unambiguously translated to a set of updates on the underlying relational database, assuming that certain key and foreign key constraints hold. In particular, we show how views defined in this subset of XQuery can be mapped to a set of relational views, thus transforming the problem of updating relational databases through XML views into a classical problem of updating relational databases through relational views.
  • Publication
    XKvalidator: A Constraint Validator For XML
    (2002-11-04) Chen, Yi; Davidson, Susan B.; Zheng, Yifeng
    The role of XML in data exchange is evolving from one of merely conveying the structure of data to one that also conveys its semantics. In particular, several proposals for key and foreign key constraints have recently appeared, and aspects of these proposals have been adopted within XMLSchema. In this paper, we examine the problem of checking keys and foreign keys in XML documents using a validator based on SAX. The algorithm relies on an indexing technique based on the paths found in key definitions, and can be used for checking the correctness of an entire document (bulk checking) as well as for checking updates as they are made to the document (incremental checking). The asymptotic performance of the algorithm is linear in the size of the document or update. Furthermore, experimental results demonstrate reasonable performance.
  • Publication
    Towards a Model of Provenance and User Views in Scientific Workflows
    (2006-07-01) Cohen, Shirley; Cohen-Boulakia, Sarah; Davidson, Susan B
    Scientific experiments are becoming increasingly large and complex, with a commensurate increase in the amount and complexity of data generated. Data, both intermediate and final results, is derived by chaining and nesting together multiple database searches and analytical tools. In many cases, the means by which the data are produced is not known, making the data difficult to interpret and the experiment impossible to reproduce. Provenance in scientific workflows is thus of paramount importance. In this paper, we provide a formal model of provenance for scientific workflows which is general (i.e. can be used with existing workflow systems, such as Kepler, myGrid and Chimera) and sufficiently expressive to answer the provenance queries we encountered in a number of case studies. Interestingly, our model not only takes into account the chained and nested structure of scientific workflows, but allows asks for provenance at different levels of abstraction (user views).
  • Publication
    Theoretical Aspects of Schema Merging
    (1991-06-25) Buneman, Peter; Davidson, Susan B; Kosky, Anthony S
    A general technique for merging database schemas is developed that has a number of advantages over existing techniques, the most important of which is that schemas are placed in a partial order that has bounded joins. This means that the merging operation, when it succeeds, is both associative and commutative, i.e., that the merge of schemas is independent of the order in which they are considered -- a property not possessed by existing methods. The technique is interactive in that users made assertions about the relationships between the nodes of the schemas to be merged. These assertions are then considered to be elementary schemas, and are combined with the schemas using precisely the same merging operation. The technique is general and can be applied to a variety of data models. It can also deal with certain cardinality constraints that arise through the imposition of keys. A prototype implementation, together with a graphical interface, has been developed.