Shankar Pal

Indexing XML data stored in a relational database

As XML usage grows for both data-centric and document-centric applications, introducing native support for XML data in relational databases brings significant benefits. It provides a more mature platform for the XML data model and serves as the basis for interoperability between relational and XML data. Whereas query processing on XML data shredded into one or more relational tables is well understood, it provides limited support for the XML data model. XML data can be persisted as a byte sequence (BLOB) in columns of tables to support the XML model more faithfully. This introduces new challenges for query processing such as the ability to index the XML blob for good query performance. This paper reports novel techniques for indexing XML data in the upcoming version of Microsoft® SQL ServerTM, and how it ties into the relational framework for query processing.

Microsoft repository version 2 and the open information model

Abstract Microsoft Repository is an object-oriented meta-data management facility that ships in Microsoft Visual Studio and Microsoft SQL Server. It includes two main components: • • A repository engine that implements a set of object-oriented interfaces on top of a SQL database system. A developer can use these interfaces to define information models (i.e., schemas) and manipulate instances of the models. • • The Open Information Model, which is a set of information models that cover object modeling, database modeling, and component reuse. The repository system is designed to meet the persistent storage needs of software tools. Its main technical goals are: • • Compatibility with Microsofts Component Object Model (COM) architecture • • Extensibility by customers and independent software vendors, so they can add behavior to objects stored by the repository engine and extend information models provided by Microsoft and others. • • Flexible and efficient versioning, configuration management, and checkout/checkin to support team-oriented activities. This paper describes the programming interface and implementation of the repository engine and the Open Information Model.

Context-based prefetch – an optimization for implementing objects on relations

Abstract. When implementing persistent objects on a relational database, a major performance issue is prefetching data to minimize the number of round-trips to the database. This is especially hard with navigational applications, since future accesses are unpredictable. We propose the use of the context in which an object is loaded as a predictor of future accesses, where a context can be a stored collection of relationships, a query result, or a complex object. When an object Os state is loaded, similar state for other objects in Os context is prefetched. We present a design for maintaining context and for using it to guide prefetch. We give performance measurements of its implementation in Microsoft Repository, showing up to a 70% reduction in running time. We describe several variations of the optimization: selectively applying the technique based on application and database characteristics, using application-supplied performance hints, using concurrent database queries to support asynchronous prefetch, prefetching across relationship paths, and delayed prefetch to save database round-trips.

Versions and workspaces in Microsoft repository

This paper describes the version and workspace features of Microsoft Repository, a layer that implements fine-grained objects and relationships on top of Microsoft SQL Server. It supports branching and merging of versions, delta storage, checkout-checkin, and single-version views for version-unaware applications.

Managing collections of XML schemas in microsoft SQL server 2005

Schema evolution is of two kinds: (a) those requiring instance transformation because the application is simpler to develop when it works only with one version of the schema, and (b) those in which the old data must be preserved and instance transformation must be avoided. The latter is important in practice but has received scant attention in the literature. Data conforming to multiple versions of the XML schema must be maintained, indexed, and manipulated using the same query. Microsoft’s SQL Server 2005 introduces XML schema collections to address both types of schema evolution.

The Impact of Multilevel Security on Database Buffer Management

Multilevel security introduces new constraints on methods for DBMS buffer management. Design issues include buffer allocation across security levels, secure page replacement, and reader/writer synchronization. We present a client/buffer manager interface with a set of synchronization guarantees that does not delay low writers in the presence of concurrent high readers, an allocation scheme that partitions slots by security level but allows buffers, underutilized at the low level, to be used by subjects at high levels using a technique we call “slot stealing.” We also propose a general page replacement algorithm and methods of synchronizing readers and writers that involve varying degrees of page replication. We use simulation to investigate the performance characteristics of the various solutions.