The Resource Description Framework (RDF) [16] is a metadata model and language recommended by the W3C for building an infrastructure of machinereadable semantics for the data on the Web, a long-term vision known as Semantic Web. In the RDF model, the universe to be modeled is a set of resources,

Abstract. In this paper, we present a method for representing the history of XML documents using Multidimensional XML (MXML). We demonstrate how a set of basic change operations on XML documents can be represented in MXML, and show that temporal XML snapshots can be obtained from MXML representations of XML histories. We also argue that our model is capable to represent changes not only in an XML document but to the corresponding XML Schema document aswell. 1

This paper presents a transaction-time HTTP server, called Apache that supports document versioning. A document often consists of a main file formatted in HTML or XML and several included files such as images and stylesheets. A change to any of the files associated with a document creates a new version of that document. To construct a document version history, snapshots of the document's files are obtained over time. Transaction times are associated with each file version to record the version's lifetime. The transaction time is the system time of the edit that created the version. Accounting for transaction time is essential to supporting audit queries that delve into past document versions and differential queries that pinpoint differences between two versions. Apache performs automatic versioning when a document is read thereby removing the burden of versioning from document authors. Since some versions may be created but never read, Apache distinguishes between known and assumed versions of a document. Apache has a simple query language to retrieve desired versions. A browser can request a specific version, or the entire history of a document. Queries can also rewrite links and references to point to current or past versions. Over time, the version history of a document continually grows. To free space, some versions can be vacuumed. Vacuuming a version however changes the semantics of requests for that version. This paper presents several policies for vacuuming versions and strategies for accounting for vacuumed versions in queries. Categories and Subject Descriptors H.3.5 [Online Information Services]: Web-based services---HTTP server; H.2.4 [Database Management Miscellaneous] Temporal--- Document versioning, transaction...

By storing the successive versions of a document in an incremental fashion, XML repositories and data warehouses achieve (i) the efficient preservation of critical information, and (ii) the ability of supporting historical queries on the evolution of documents and their contents. In this paper, we present efficient techniques for managing multiversion document histories and supporting powerful temporal queries on such documents. Our approach consists in (i) concisely representing the successive versions of a document as an XML document that implements a temporally grouped data model, and (ii) using XML query languages, such as XQuery, to express complex queries on the content of a particular version, and on the temporal evolution of the document elements and their contents. We show that the data definition & manipulation framework of XML & XQuery can support temporal models and historical queries significantly better than the traditional framework of Relational Tables & SQL. To demonstrate this point, we investigate how to express complex queries on the history of relational tables published as XML data.

There is much current interest in publishing and viewing database-resident data as XML documents. In fact, such XML views of the database can be easily visualized on web browsers and processed by web languages, including powerful query languages such as XQuery. As the database is updated, its external XML view also evolves. In this paper, we investigate the problem of representing the evolution history of such a view as yet another XML document, whereby the complete history of the database can also be visualized on web browsers, processed by web languages, and queried using powerful query languages such as XQuery. We investigate various approaches used for publishing relational data, and identify and select those which are best for representing and querying database histories. We show that the selected representations make it easy to formulate in XQuery temporal queries that are difficult to express using SQL on database relations. Finally, we discuss briefly the storage organization that can be used to support these queries efficiently.

Different models have been proposed recently for representing temporal data, tracking historical information, and recovering the state of the document as of any given time, in XML documents. We address the problem of indexing temporal XML documents. In particular we show that by indexing continuous paths, i.e. paths that are valid continuously during a certain interval in a temporal XML graph, we can dramatically increase query performance. We describe

Past research work on modelling and managing temporal information has, so far, failed to elicit support in commercial database systems. The increasing popularity of XML and XQuery offers a unique opportunity to change this situation, inasmuch as these support temporal information much better than relational tables and SQL. This is the important conclusion claimed in this paper where we show that valid-time, transaction-time, and bitemporal databases can be naturally viewed in XML using temporally-grouped data models; then we show that complex historical queries, that would be very di#cult to express in SQL on relational tables, can now be easily expressed in standard XQuery on such XML-based representations. We first discuss the management of transaction-time and valid-time histories and then extend our approach to bitemporal histories. The approach can be generalized naturally to support the temporal management of arbitrary XML documents and queries on their version history.

Abstract. In this paper we extend the XPath data model and query language to include valid time. XPath is a language for specifying locations within an XML document. We extend XPath’s data model by adding to each node a list of disjoint intervals or instants that represents the valid time. The valid time for a node is constrained to be a subset of the valid time for a node’s parent. We extend the XPath query language with an axis to access nodes in a valid-time view of the valid time for a node. The view is a calendar-specific formatting of the valid time in XML. By rendering the time in XML, we can reuse nontemporal XPath to extract the desired information within a valid-time axis. The extension is fully backwards-compatible with XPath. 1

There is much current interest in publishing and viewing databases as XML documents. The general benefits of this approach follow from the popularity of XML and the tool set available for visualizing and processing information encoded in this universal standard. In this paper, we explore the additional and unique benefits achieved by this approach on temporal database applications. We show that XML views combined with XQuery can provide surprisingly effective solutions to the problem of supporting historical queries on past content of database relations and their evolution. Indeed, using XML, the histories of database relations can be naturally represented by temporally grouped data models. Thus, we identify mappings from relations to XML that are most conducive to modeling and querying database histories, and show that temporal queries that would be very difficult to express in SQL can be easily expressed in standard XQuery.

There is much current interest in publishing and viewing databases as XML documents. The general benefits of this approach follow from the popularity of XML and the tool set available for visualizing and processing information encoded in this universal standard. In this paper, we explore the additional and unique benefits achieved by this approach on temporal database applications. We show that XML with XQuery can provide surprisingly e#ective solutions to the problem of supporting historical queries on past content of database relations and their evolution. Indeed, using XML, the histories of database relations can be naturally represented by temporally grouped data models. Thus, we identify mappings from relations to XML that are most conducive to modelling and querying database histories, and show that temporal queries that would be di#cult to express in SQL can be easily expressed in standard XQuery. This approach is very general, insofar as it can be used to store the version history of arbitrary documents and, for relational databases, it also supports queries on the evolution of their schema.