An XML database is a type of database designed to store, query, and manipulate data in XML format. Unlike traditional relational databases that store data in rows and columns, XML databases treat XML documents as first-class citizens, preserving their tree-like structure.
Key Characteristics
- Stores data as hierarchical documents (XML trees)
- Supports XPath and XQuery for querying
- Useful for semi-structured or hierarchically structured data
- Can be native (XML is stored as-is) or XML-enabled (XML is stored in relational tables)
Types of XML Databases
Native XML Databases
- Store XML documents directly, preserving their structure
- Querying is optimized for XML with XQuery or XPath
- Example: BaseX, eXist-db, Sedna
XML-Enabled Relational Databases
- Traditional RDBMS with XML support via columns or data types
- Parse XML and map it to relational tables or store as XML strings
- Example: PostgreSQL (XML type), Oracle XML DB, SQL Server
Use Cases
- Applications where data is already in XML (e.g., configuration, documents, SOAP)
- Metadata repositories or publishing systems
- Storing scientific, technical, or legal documents with deeply nested structures
- Systems that rely on data interchange formats (XML, XSLT, etc.)
Pros and Cons
Advantages
- Ideal for document-centric or hierarchical data
- Schema flexibility: no fixed table definitions required
- Rich querying using XPath and XQuery
- Native support for XML transformations (XSLT)
Disadvantages
- Slower than RDBMS for flat, structured data
- Complex indexing and performance tuning
- Limited adoption compared to NoSQL or relational databases