Davidson, Susan B

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  • 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.
  • 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
    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
    Consistency in a Partitioned Network: A Survey
    (1984) Davidson, Susan B; Garcia-Molina, Hector; Skeen, Dale
    Recently, several strategies for transaction processing in partitioned distributed database systems with replicated data have been proposed. We survey these strategies in light of the competing goals of maintaining correctness and achieving high availability. Extensions and combinations are then discussed, and guidelines for the selection of a strategy for a particular application are presented.
  • Publication
    Facilitating Transformations in a Human Genome Project Database
    (1993-12-08) Davidson, Susan B; Kosky, Anthony S; Eckman, B.
    Human Genome Project databases present a confluence of interesting database challenges: rapid schema and data evolution, complex data entry and constraint management, and the need to integrate multiple data sources and software systems which range over a wide variety of models and formats. While these challenges are not necessarily unique to biological databases, their combination, intensity and complexity are unusual and make automated solutions imperative. We illustrate these problems in the context of the Human Genome Database for Chromosome 22 (Chr22DB), and describe a new approach to a solution for these problems, by means of a deductive language for expressing database transformations and constraints.
  • Publication
    Timed Atomic Commitment
    (1989-10-01) Davidson, Susan B; Lee, Insup; Wolfe, Victor
    In a large class of hard-real-time control applications, components execute concurrently on distributed nodes and must coordinate, under timing constraints, to perform the control task. As such, they perform a type of atomic commitment. Traditional atomic commitment differs, however, because there are no timing constraints; agreement is eventual. We therefore define timed atomic commitment (TAC) which requires the processes to be functionally consistent, but allows the outcome to include an exceptional state, indicating that timing constraints have been violated. We then present centralized and decentralized protocols to implement TAC and a high-level language construct that facilitates its use in distributed real-time programming.
  • Publication
    Modeling Reliable Distributed Real-Time Programs
    (1988-05-01) Davidson, Susan B; Wolfe, Victor; Lee, Insup
    A model for distributed hard real-time programs should incorporate real-time characteristics and be capable of analyzing time-related reliability issues. We introduce a model called the Real-Tie Selection/ Resolution (RT-SIR) Model with these capabilities and demonstrate it by example.
  • Publication
    Partial Computation in Real-Time Database Systems: A Research Plan
    (1988-10-01) Davidson, Susan B; Lee, Insup
    State-of-the-art database management systems are inappropriate for real-time applications due to their lack of speed and predictability of response. To combat these problems, the scheduler needs to be able to take advantage of the vast quantity of semantic and timing information that is typically available in such systems. Furthermore, to improve predictability of response, the system should be capable of providing a partial, but correct, response in a timely manner. We therefore propose to develop a semantics for real-time database systems that incorporates temporal knowledge of data-objects, their validity, and computation using their values. This temporal knowledge should include not just historical information but future knowledge of when to expect values to appear. This semantics will be used to develop a notion of approximate or partial computation, and to develop schedulers appropriate for real-time transactions.
  • Publication
    Updating Complex Value Databeses
    (1998-02-23) Liefke, H.; Davidson, Susan B.
    Query languages and their optimizations have been a very important issue in the database community. Languages for updating databases, however, have not been studied to the same extent, although they are clearly important since databases must change over time. The structure and expressiveness of updates is largely dependent on the data model. In relational databases, for example, the update language typically allows the user to specify changes to individual fields of a subset of a relation that meets some selection criterion. The syntax is terse, specifying only the pieces of the database that are to be altered. Because of its simplicity, most of the optimizations take place in the internal processing of the update rather than at the language level. In complex value databases, the need for a terse and optimizable update language is much greater, due to the deeply nested structures involved. Starting with a query language for complex value databases called the Collection Programming Language (CPL), we describe an extension called CPL+ which provides a convenient and intuitive specification of updates on complex values. CPL is a functional language, with powerful optimizations achieved through rewrite rules. Additional rewrite rules are derived for CPL+ and a notion of "deltafication" is introduced to transform complete updates, expressed as conventional CPL expressions, into equivalent update expressions in CPL+. As a result of applying these transformations, the performance of complex updates can increase substantially.
  • 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.