XBRL (extensible Business Reporting Language) is an XML based standard for electronic data exchange and communication of business financial documents and reports among government bodies, regulators, financial institutions and reporting entities. In this paper, we analyze the XBRL model from a perspective of data management to show why XBRL has created a new emerging vertical domain of database applications that offer opportunities and technical challenges for the database community. We outline the concept of an XBRL repository as a data hub to store and process collections of XBRL documents while maintaining document integrity based on XBRL semantics, providing document manageability, operational completeness and XBRL dictionary, query and business intelligence services. We then share our experiences of building the main components of the XBRL repository using the Oracle XML enabled RDBMS that leverages both XML and relational technologies as a backbone to host industrial strength XBRL applications. We also highlight technical challenges and potential solutions to each of the components. Finally we propose the potential of leveraging the XBRL data model concept for providing XML data normalization and XML having multi-hierarchy.

RDBMS provides best performance for querying structured data that starts out with a well-defined schema. However, such a 'schema first, data later' approach does not work for unstructured data or data without much structure. Therefore, RDBMS typically stores such data without any schema in LOB columns (for example, Character Large Object (CLOB) or Binary Large Object (BLOB) columns) and provides Information-Retrieval (IR) style, keyword-based search capability over these LOB columns. Lately, XML as a native datatype (XMLType) in RDBMS has been introduced via the SQL/XML standard. Semi-structured data with or without any schema can be stored into such XMLType columns, and XQuery provides query capability over them. In particular, XQuery full text specification provides the capability of searching keywords within document context. Such full context-aware text search capability is more powerful than pure keyword search, since the user can now provide fine-grained context in which the keywords should occur. However, XML with XQuery full text searching requires that the user first convert her text data into XML and store them into XMLType column. Such massive physical data migration with possible loss of document fidelity and its potential impact on existing production environments are often expensive enough that users are reluctant to adopt the XML/XQuery approach.

There has been a lot of research and industrial effort on building XQuery engines with different kinds of XML storage and index models. However, most of these efforts focus on building either an efficient XQuery engine with one kind of XML storage, index, view model in mind or a general XQuery engine without any consideration of the underlying XML storage, index and view model. We need an underlying framework to build an XQuery engine that can work with and provide optimization for different XML storage, index and view models. Besides XQuery, RDBMSs also support SQL/XML, a standard language that integrates XML and relational processing. There are industrial efforts for building hybrid XQuery and SQL/XML engines that support both languages so that users can manage and query both relational and XML data on one platform. However, we need a theoretical framework to optimize both SQL/XML and XQuery languages in one RDBMS. In this paper, we show our industrial work of building a combined XQuery and SQL/XML engine that is able to work and provide optimization for different kinds of XML storage and index models in Oracle XMLDB. This work is based onXML extended relational algebraas the underlying tuple-based logical algebra and incorporates tree and automata based physical algebra into the logical tuple-based algebra so as to provide optimization for different physical XML formulations. This results inlogical and physical rewritetechniques to optimize XQuery and SQL/XML over a variety of physical XML storage, index and view models, including schema aware object relational XML storage with relational indexes, binary XML storage with schema agnostic path-value-order key XMLIndex, SQL/XML view over relational data and relational view over XML. Furthermore, we show the approach of leveragingcost based XML physical rewritestrategy to evaluate different physical rewrite plans.

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