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Natix Done by Asmaa Hassanain CSC 5370 Dr. Hachim Haddoutti 12/8/2003 Contents XML data management Techniques What is Natix Natix Architecture Storage Layer: Logical Data Model Mapping between XML and the Logical Model XML page Interpreter Storage Formater XML segment mapping for large trees Index Structures Natix Physical Algebra Example Plans To do... CSC 5370 XML and Data Management 2 XML data management Techniques Map data to relational database But: Store data as a plain text file Unnormalized relations But: Data as centric view: Large number Storedata objects Need to parse the entire file for of tables But: processing every query Designing Nativecentric XML database Document all OOD systems are view: not enough systemsinformantion from scratch a single data item developed to in provide efficient querying capabilities (e.g. CLOB) CSC 5370 XML and Data Management 3 Natix CSC 5370 XML and Data Management 4 What is Natix? Natix is a native XML Repository Proposed by Kanne and Moerkotte at University of Mannheim (Germany) Natix requires Linux to run (kernel 2.2.16 or later, or 2.4.*), with CODA support enabled in the kernel. Still under development CSC 5370 XML and Data Management 5 Natix Architecture CSC 5370 XML and Data Management 6 Natix Architecture Binding Layer: map between the Natix Engine Interface and different application interfaces CSC 5370 XML and Data Management 7 Natix Architecture e. g. NatixFS: File system interface – Natix can be mounted like an ordinary file system Allows to view XML tree as a file system tree Importing a document – just copy it to a directory, e.g. cp bib.xml /natix Exporting a document – just open it, e.g. more /natix/bib.xml Removing a document – just delete a file, e.g. rm /natix/bib.xml XPath expressions – just use it as file name, e.g. more /natix/{%%title} CSC 5370 XML and Data Management 8 Natix Architecture Service Layer: Provides all DBMS functionality required in addition to simple storage and retrieval Natix Engine Interface Query execution engine Query compiler Transaction manager Object manager CSC 5370 XML and Data Management 9 Natix Architecture Natix Engine Interface: The interface through which the database services communicate with each other and with applications provides a unified facade to specify requests to the database system. CSC 5370 XML and Data Management 10 Natix Architecture Query compiler: translates queries expressed in XML query languages into optimized query execution plans CSC 5370 XML and Data Management 11 Natix Architecture Query execution engine: evaluates queries Interprets the plan passed by the query compiler Able to execute all queries expressible in a typical XML query language like XQuery CSC 5370 XML and Data Management 12 Natix Architecture Transaction management : contains classes that provide ACIDstyle transactions + Components for recovery adapt the ARIES protocol for recovery For synchronization, an S2PLbased scheduler is introduced CSC 5370 XML and Data Management 13 Natix Architecture Storage Layer: manages all persistent data structures and their transfer between main and secondary memory . contains classes for efficient XML storage, indexes and metadata storage. manages the storage of the recovery log and controls the transfer of data between main and secondary storage. accesses raw disks or file system files and provides a memory space divided into segments, which are a linear collection of equal-sized pages. CSC 5370 XML and Data Management 14 Storage Layer: Logical Data Model Logical Data Model: logical tree New nodes can be inserted as children or siblings of existing nodes Any node can be removed Individual documents are represented as ordered trees CSC 5370 XML and Data Management 15 Mapping between XML and the Logical Model A small wrapper class is used to map the XML model with its node types and attributes to a simple tree model and vice versa: Elements are mapped one to one to tree nodes of Logical Data Model Atributes are mapped to child nodes of an additional attribute container child node The name of referenced entities are retained in special internal nodes CSC 5370 XML and Data Management 16 XML page Interpreter Storage Formater The logical data tree is partitioned into subtrees Each sudtree is stored in a single record of variable lenght Each record contains a pointer to the record containing the parent node and the document identifier CSC 5370 XML and Data Management 17 XML page Interpreter Storage Formater Subtrees of original XML document are stored together in a single physical record clusters connected subtrees of the document tree into large records and represents intra-record references differently from inter-record references The inner structure of the subtrees is retained CSC 5370 XML and Data Management 18 XML segment mapping for large trees Proxy nodes refer to connected subtrees not stored in the same record Helper aggregate nodes group together a subset of children of a node CSC 5370 XML and Data Management 19 Index Structures Natix uses two Index Structures: Full text index framework (inverted files): store lists of document Index eXtended Access Support Relation references to indicate Map search terms in to which list identifier and List Manager Preserves the parent/child, ancestor/ documents search terms appear store these mappings persistenly Maps the list identifiers to the actual descandant, and preceding/following FragmentedList lists (managing the directory offor the Provides the main interface relationships between nodes Lists are divided to fragments that fit the on a ContextDescription inverted file) page to +combined linked + can be traversed user work together with inverted files The XASR with a full text Establishes the actual representation sequentially index a powerful in provides which data is storedmethod in a list It manages all the fragments of one list and to search on contentens of nodes control insertions and deletions on this list CSC 5370 XML and Data Management 20 Natix Physical Algebra ‘Let’, ‘for’, ‘where’ and ‘return’ in XQuery are supported ‘Select’, ‘map’, ‘join’, ‘grouping’ and ‘sort’ operations are performed by standard algebraic operators borrowed from relational context ‘D-join’ and ‘unary and binary grouping’ are borrowed from the object oriented context CSC 5370 XML and Data Management 21 Natix Physical Algebra Scan operations: e. g. ExpressionScan ExpressionScan: generates a tuple containing the root of the document identified by its name by evaluating a given expression UnnestMap is used to generate variable bindings for XPath expressions e.g./a//b/c UnnestMap$4=child($3,c)( UnnestMap$3=desc($2,b)( UnnestMap$2=child($1,a)([$1]))) ‘BA-Map’, ‘FL-Map’, ’Groupify-GroupApply’ and ‘NGroupify-NGroupApply’ are use to construct the XML result CSC 5370 XML and Data Management 22 Example Plans (1): This query retrieves the title and the year for all recent books CSC 5370 XML and Data Management 23 Example Plans (2): CSC 5370 XML and Data Management 24 To do... Support for functions inside XPath expressions Cannot import DTDs as of now Support for different character encodings Support for XML namespaces preparing for the launch of the first full commercial end-user release of Natix that may support all these features CSC 5370 XML and Data Management 25 Questions ? CSC 5370 XML and Data Management 26 References Natix: A Technology Overview: http://pi3.informatik.unimannheim.de/publications.html#79 Efficient storage of XML data: http://pi3.informatik.unimannheim.de/publications.html#79 Anatomy of a Natix XML base Management System: http://pi3.informatik.unimannheim.de/publications.html#79 Alebraic XML Construction and its Optimization in Natix: http://pi3.informatik.unimannheim.de/publications.html#79 Data ex machina: www.dataexmachina.de/natix.html CSC 5370 XML and Data Management 27 Thank You CSC 5370 XML and Data Management 28