Data Centric Integrated Framework on Hotel Industry. Bridging XML to Relational Database

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1 Data Centric Integrated Framework on Hotel Industry Bridging XML to Relational Database Introduction extensible Markup Language (XML) is a promising Internet standard for data representation and data exchange due to its flexible structure to share common information and data in World Wide Web [1]. Hence, it is vital to have competent and effective way of storing and querying XML document. There are three main approaches to store XML data [2][3][4][5]. First, storing XML data in repositories designed for semi-structured data. Second, storing in object-oriented database and finally, storing data in relations via relational database. In this paper, we focus on storing and querying XML data based on Relational Database Management Systems (RDBMS). It is vital for we to elect the most approach mapping scheme for proficient XML processing. In conjunction with this, a mapping scheme must ensure that it maintains the important relationship information in the table so that query processing for both storage and retrieval will be consistent and efficient. The mapping approach needs to maintain the ancestor-descendant, parent-child and sibling relationship as well as level information for better query processing. Research Motivation As we all known, there are two types of user queries being in used which are full-text and structural queries. Full-text query is a keyword-based search where users will only need to enter one or more keywords and the query processing will be based on the words entered. Structural query is where user enters a query with other interrelated information. Many of the existing mapping techniques fail to sustain structural queries because the information about the connection among the nodes is not maintained in the tables. As a result, query retrieval will be inconsistent University Multimedia, 2010 Page 1

2 and the mapping approach will not be able to cater user s request with multiple combinations of information. Therefore, a good mapping scheme which can preserve the connections among the nodes is needed for competent XML processing. Literature Review There have been lots of studies and researches done so far with the aim to propose a better scheme from the existing mapping methods. In this section, we show related work pertaining to mapping approaches and their table schema. 1) Edge Approach: The most simplest and straightforward approach is the Edge approach [3] which stores the XML attributes and elements in a single Edge table. Edge table records the source of an element, the ordinal which preserves the order of an element in the XML tree, name of the attribute, flag which indicates if an object is an inter-object reference or points to a value and target object of an attribute. Therefore, the structure of Edge table is Edge(source,ordinal,name,flag,target). 2) Attribute Approach: Attribute approach [3] groups all the attributes with the same name into a single table. Consequently there will be as many Attribute tables as different attribute names appear in the XML document. The structure of the Attribute table is A name (source,ordinal,flag,target) where name refers to the name of the attribute and the definition for the other columns (source, ordinal,flag,target) is the same as in the Edge approach. 3) Universal Approach: Universal [3] technique maintains separate column for all the attributes that occur in the XML document. Universal table is structured as Universal (source, ordinal n1, flag n1, target n1, ordinal n2, flag n2, target n2,,ordinal nk, flag nk, target nk ). This approach causes lots of redundancies for multi-valued attributes. University Multimedia, 2010 Page 2

3 4) Univ orm Approach: UnivNorm or Normalized Universal [3] approach was proposed to fix the problem faced in Universal approach. The difference between these two approaches is UnivNorm stores multi-valued attributes in a separate table which is called as the Overflow table. As such there is only one row per an object stored in UnivNorm table and the table is normalized. The structure of the Overflow table is Overflow n1 (source, ordinal, flag, target),, Overflow nk (souce, ordinal, flag, target). 5) XRel approach: XRel [6] is a path-based approach, decomposes an XML document into nodes based and stores the information in relational tables according to the node types as well as the simple-path expression from the root node to the current node. Basically, there are four relational schemas in XRel which are as follows. Element(docID, pathid, start, end, index, reindex) which stores the element, Attribute (docid, pathid, start, end, value) store the attributes, Text (docid, pathid, start, end, value) with the purpose of storing data and lastly, Path (pathid, pathexp) which is used to store the simple-path expression. The pathid in Element, Attribute and Text tables refers to the pathid in Path table which also serves as the foreign key of the tables. 6) XParent approach: XParent [7] is a model-mapping approach models XML document as an ordered tree [5]. This approach maps the ordered tree into four relational tables which are LabelPath (ID, Len, Path) which stores the label path and each label path is identified using a unique ID. DataPath (Pid, Cid) which maintains parent-child relationship, Element (PathID, Did, Ordinal) stores element information and Data (PathID, Did, Ordinal, Value) stores data in the table. PathID in Element and Data tables are the foreign key to ID in the LabelPath table. The Did which stands for Data-path-id is a node identifier which also serves as a unique data-path identifier for the data-path ended at the node itself. This approach also maintains separate table to store ancestor information (stores ancestordescendent relationship) which serves as an advantage of this method. Approach Disadvantages Advantages Edge -Level information is not stored -Simplest mapping technique which stores in the table therefore it is quite an XML document in single Edge table. University Multimedia, 2010 Page 3

4 Attribute Universal Univ orm XRel XParent difficult to determine the ancestor-descendant relationship between the nodes -Unable to process a query with the combinations of parent-child and ancestor-descendant edges -Creates one table for each attribute therefore number of table depends on the number of distinct attributes in XML document -Requires many joins for complex query -Causes redundancy for multivalued attributes and the table is not normalized -Deleting an attribute in XML document requires massive updates of ordinal attribute in the Universal table -Deleting an attribute in XML document requires massive updates of ordinal attribute in the Universal and Overflow table -Too many tables which require excessive joins for complex query and query with various combinations. -Too many tables require excessive joins for complex query and query with various combinations. -Tables which store parent-child and ancestor-descendant relationships may grow larger depending on the complexity of XML document and eventually increases the size of database. -Insertion and deletion of an object or attribute is simple. -Insertion and deletion of an object or attribute is simple and easy -Stores XML document in single Universal table. -Deletion of an object is simple -Normalized approach which inserts one row per attribute of an object. -If there exist a multi-valued attribute with cardinality n, it stores n rows in Overflow table. -Region information stored in the table which allows the processing of a query with the combination of ancestordescendant and parent-child edges -Since table schema is based on the node types, insertion and deletion of an attribute or object are simple. -Maintains path information in separate table which will be referenced by other tables and eventually reduces database size. -Maintains parent-child and ancestordescendant relationship between nodes in separate tables therefore, the processing of a query with the combination of ancestordescendant and parent-child edges are simple. -Maintains path information in separate table which reduces database size and avoid redundancy in tables. s-xml -Calculation required to -Only two tables involved therefore there University Multimedia, 2010 Page 4

5 determine ancestor-descendant relationship will be less joins required for query processing -Order information and parent-child information stored efficiently -Queries involving parent-child and ancestor-descendant edges can be processed easily though ancestordescendant relationship Table 1: Advantages and disadvantages of the mapping approaches Problem Formulation Relationship among the nodes needs to be preserved for XML data storage and retrieval using Relational Database Management System. Thus, a good mapping scheme is to be proposed and implemented. Research Methodology This project is divided into four main sections: - (1) Investigation on current mapping/integration technique. Using the related literatures and understanding in the current query processing technique, we outline each mapping technique advantages and limitations. (2) Design of conceptual framework/solution for XML integrator The framework is composed of three main components, namely, the XML Parser, the XML Encoder, and the Data Manager as shown in figure below. XML document must always be parsed, checked for well-formedness and validated before data transfer and exchange can take place. In XML Encoder, XML documents are encoded as a set of streams labeled with robust and dynamic labeling scheme to support dynamic update. The Data Manager serves as the data repository. (3) Experimentation and system development University Multimedia, 2010 Page 5

6 The development of the Integrator Architecture will basically based on Software Development Life Cycle (SDLC) and Database Development Life Cycle (DBLC). (4) Testing and evaluation on prototype. The prototype developed in (3) is to be tested for performance comparison using real and synthetic datasets obtained from various benchmarking tools. XML Document XML Parser Data Table Figure 1: Example of XML processing Throughout the research process, a mapping approach was proposed namely s-xml + which is an extension of s-xml. This mapping technique that we propose is based on two tables which are the ParentTable and ChildTable. The ParentTable stores the information about the parent nodes (except for the leaf nodes). The ChildLabel stores the information about the leaf nodes. The schemas for these two tables are as follows: ParentTable (Id ode, p ame,c ame, LParent, SelfLabel) where: - IdNode is used to uniquely identify the nodes stored in the ParentTable - pname is the node name of the parent node - cname is the node name of the child node - LParent refers to the combination of the level and the label of the parent node - SelfLabel indicates the local code of the node. ChildTable (Id ode, Level, Child, LParent,value) where: - IdNode uniquely identifies the nodes store in the ChildTable - Level indicates the level of the node in XML document - Child column stores the local code of the label University Multimedia, 2010 Page 6

7 - LParent stores the parent label with reference to LParent attribute in the ParentTable. - Value stores the taxt value of the leaf node This mapping technique maintains the relationship among the nodes in the database precisely which supports both full-text and structural queries. The performance of this technique will be compared with other approaches such as the Edge, Attribute and s-xml approaches. Activity Literature Review Designing Conceptual Framework Refinement of conceptual Framework Development Testing Evaluation of Refinement of Reports Writing and Documentation 2009/ 2010 Sept Oct ov Dec Jan Feb Mar Apr May Jun Jul Aug Sept Activity Literature Review Designing Conceptual Framework Refinement of conceptual Framework Development Testing 2010/ 2010 Oct ov Dec Jan Feb Mar Apr May Jun Jul Aug Sept University Multimedia, 2010 Page 7

8 Evaluation of Refinement of Reports Writing and Documentation References [1] Haifeng Jiang, Hongjun Lu, Wei Wang and Jeffrey Xu Yu, Path Materialization Revisited: An Efficient Storage Model for XML Data, In Proc. of ADC, [2] Feng Tian, David J. DeWitt, Jianjun Chen, Chun Zhang, The Design and Performance Evaluation of Alternative XML Storage Strategies, University of Wisconsin, Madison [3] Daniela Florescu and Donald Kossmann, Storind and Quering XML Data Using an RDBMS, IEEE Data Engineering Buletin,1999, pp [4] Laifur Khan, Yan Rao, A Performace Evaluation of Storing XML Data in Relational Database Management Systems, ACM 2001 [5] F.Tian, D.J.Dewitt, J.Chen, C.Zhang, The Design and Performace Evaluation of Alternative XML Storage Strategies, SIGMOD [6] Masatoshi Yoshikawa amd Toshiyuki Amagasa, XRel: A Path-Based Approach to Storage and Retrieval of XML Documents using Relational Databases,In ACM Transactions on Internet Technology (TOIT), [7] Haifeng Jiang, Hongjun Lu, Wei Wang and Jeffrey Xu Yu, XParent: An Efficient RDBMS- Based XML Database System, In Proc. of ICDE, University Multimedia, 2010 Page 8