XML is often used to represent objects that expose different sets of properties. This "property bag" scenario is a prominent use case for the XML support added to Microsoft SQL Server 2005. However, each property extraction in our initial implementation executed as a separate relational subquery. This was problematic since query performance became unacceptable even for small data sizes when returning an increasing number of properties. We addressed this problem by developing an interesting generalization of common subexpressions. This paper makes the following contributions: (1) it introduces an equivalence rewrite for relational query optimization to fold similar scalar subqueries. Several such subqueries are merged into a single equivalent multi-column subquery using both predicate disjunction and rowset pivoting. The rewrite operates at the logical operator level which makes it equally applicable to XML queries and SQL queries. (2) We explain how this optimization can be applied to the XML property bag scenario and how it has been implemented for the XML index in Microsoft SQL Server 2005. (3) An experimental investigation with Microsoft SQL Server 2005 studies the performance characteristics of the optimization. It shows that the optimization yields significant performance improvements - without limiting essential optimizer execution plan choices.

We introduce a hierarchical labeling scheme called ORDPATH that is implemented in the upcoming version of Microsoft® SQL Server™. ORDPATH labels nodes of an XML tree without requiring a schema (the most general case---a schema simplifies the problem). An example of an ORDPATH value display format is "1.5.3.9.1". A compressed binary representation of ORDPATH provides document order by simple byte-by-byte comparison and ancestry relationship equally simply. In addition, the ORDPATH scheme supports insertion of new nodes at arbitrary positions in the XML tree, their ORDPATH values "careted in" between ORDPATHs of sibling nodes, without relabeling any old nodes.

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.

This paper discusses the security issues involved in log management for a multilevel secure database system and presents a design and implementation of a prototype multilevel secure log manager. The main goal of a log manager is to provide high bandwidth and low flush latency. We examine the performance of our design, by observing the flush latency and log bandwidth. We also informally evaluate the security of our approach.

We address the problem of recovery in object-oriented data-bases from considerations of the semantics of committed transactions and the efficiency of recovery procedures. The recovery strategy used is update-in-place. We show that efficient recovery procedures should allow transactions to abort independently of one another by executing inverse operations. We refer to these requirements collectively as the recovery isolation property. We present a formal definition of recovery isolation and prove that schedules possessing this property do not suffer from rollback dependencies. Recovery isolation is useful in constructing concurrency control protocols that go beyond commutativity, and in parallel and high performance database systems. We define the notion of strict schedules for object-oriented databases as an extension of the analogous definition for read and write operations. We show that strict schedules possess the recovery isolation property.