Data::Stag
This perl module is for querying and manipulating complex data as recursively nested tag/value pairs (Structured tags or Simple Tree aggreggates). Procedural and object-oriented modes are supported. Tags can be accessed by autogenerated accessor methods.
XML is a hierarchical data format, so this module can be used as an XML parser/writer. Other hierarchical formats are supported, including lisp S-Expressions (i.e. SXML) and indented-text.
Construction of parsers, transformers and writers is simplified with structured tag events, similar to and compatible with SAX.
As well as being a useful module for perl developers, this module also comes with a number of useful scripts for manipulating stag data.
At this time there is only a perl implementation, Data::Stag, but C and Lisp implementations are planned.
DBIx::DBStag
This module is for conversion between relational representations and hierarchical tag-value pairs, i.e. Stag trees, or XML.
Querying: SQL query results are automatically decomposed into the relations used in the query, and a hierarchical structure is inferred. This allows you to go from multi-table joins to deeply nested hierarchical representations that capture the foreign key data in the database.
This modules also allows you to create SQL templates - a powerful way of reusing complex SQL statements.
Storage: Stag trees can be stored in a relational database with a minimum of metadata. There are also scripts to help with construction of ad-hoc normalised relational databases from XML sources.