XML and XML-Enabled Databases Paper Example

Introduction

The increasing popularity of XML data and the increasing need for extensive storage, retrieval, and manipulation of XML-based data have accelerated research on XML as well as XML-enabled database systems. The main challenge as discussed by (Saba, Shahab, Abdolrahimpour, Hakimi & Moazzam, 2017) have been on the manner in which data and information can be exchanged between different types of applications and e-business systems independently. With research, the eXtensible Markup Language (XML) has proved to be the most potential standard conforming to these needs. In this document, we critically evaluate and assess XML and XML-enabled databases with the primary objective of identifying and discussing the main issues that may arise in the storage, retrieval as well as manipulation of data stored in XML-enabled database systems.

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XML proposes a new model of describing non-textual documents through the use of non-predefined tags. The language makes use of tags, formally known as elements, in describing the data enclosed. Owing to the ability of the users to generate custom tags for the description of the data, XML has developed and quickly spread as one of the major forms and models of data exchange (Saba, Shahab, Abdolrahimpour, Hakimi & Moazzam, 2017). Among the main advantages of XML that have facilitated its growing popularity include the heterogeneity of the data records, extensibility as it allows the application of different types of data and the flexibility of the language. XML can be argued as a standard format applied in cross-platform data exchange as well as integration. It has become a normal and popular thing to find applications producing new data directly in XML format or converting the already existing information from the traditional form to XML format.

Storage of XML data into XML-Enabled Databases

Depending on the particular attributes of the XML applications, the existing XML storage methodology can adequately be categorised into two main groups; text-centric and data-centric applications. Text-centric applications primarily make use of a particular file system for the storage of data (Eito-Brun, 2018). The data to be stored is primarily broken down into smaller units, with each unit stored as a separate file. Such applications will then provide search alternatives that enable the users to find a particular set of data specifically. Although this approach greatly assists in simplifying the storage of XML data, it is marred by several challenges and limitations (Haw, & Chong, 2016). The first challenge is that the storage of XML data in the text makes it rather challenging to develop the data manipulation processes. Secondly, the mapping between the individual logical units towards the individual files of data renders it challenging to view and utilise the data in a different manner and perspective (Eito-Brun, 2018). In the understanding of these challenges, this approach is only applicable when only limited services are required from the database management system.

The send category is the data-centric category. These applications often use data that is highly structured, primarily sourced from relational databases (Eito-Brun, 2018). In these applications, XML is primarily used as a tool for publishing the data to the web or to retrieve and provide the data in a self-descriptive manner, instead of making use of relational data files. This category of applications relies on the use of RDBMS as their main approach to data storage. All data that is collected through the use of XML databases must be eventually stored in the RDBMS particularly in instances when persistence and consistency are required. In either of the two approaches, it is clear that XML is primarily utilized as an interface and not a database management system (Eito-Brun, 2018). It is an interface between the actual underlying DBMS, primarily a relational DBMS, and the application or the users who access the data.

XML-Enabled Databases are primarily applied in the configurations of where XML is the primary format for the exchange of data between the underlying database system and another database or application. One of the major attributes of the methods applied by XML-Enabled Databases for data storage is that they apply data models other than XML (Alahmari & Pardede, 2012). Most often, the relational data model is used to implement the storage function in XML-enabled databases. In the storage operation, every situation of the selected data models is mapped to one or more than one instances of the XML data model. It is worth noting that in XML-enabled databases, XML documents are primarily used as a data exchange format and do not have any particular identity within the database itself. The format means that XML documents normally have significance only when the data has not yet been stored in the database; otherwise, the documents are discarded as soon as the data is stored in the databases. Similarly, when needed, XML documents are created instantly using the results of a query. The document is then discarded as soon as the client who requested it uses it.

The urge towards the support of XML data storage, retrieval as well as manipulation through the utilisation of the existing data structures, has been the main primary reason for the adoption of XML-enabling layer over the existing relational database management systems (Alahmari & Pardede, 2012). For a relational database, the best option for implementation of stored procedure has been identified to be the active XML project. The XML document can embed calls to a web service inside the XML document as it performs the transfer of information over the web.

The different types of XML databases

As mentioned earlier, the field of XML databases is relatively new and relatively evolving at a rapid rate. It is therefore not easier to explain the existing boundaries between the different types of XML databases. A lot of difficulties are experienced when it comes to the classification of the XML documents as either data-centric or document-centric. The XML database can be categorised into three main types which include the native XML database, the XML Enabled database and hybrid XML database(Alahmari & Pardede, 2012). The native XML databases are characterized by their ability to define the logical models for an existing XML document. The native XML database then stores and retrieves the document according to the defined model differs from the data contained in the XML document. The fundamental unit of a logical store for a native XML database is an XML document. The XML document can hence be compared to a row in a table for a relational database. The native databases are not required to have specific physical storage model. The proprietary storage format, the object-oriented database or relational models can be used.

The XML enabled database can be differentiated from other models because of its added XML mapping layer. The extra mapping layer can be provided by either the third party of the database vendor. The added mapping layer manages the storage and retrieval of XML data. The original XML meta-data can be lost under a situation where the data mapped into a database is again mapped into application-specific formats (Corbin, Muldner, & Miziolek, 2014). The data manipulation may occur through the XML specific technology or a different database technology such as SQL. An XML enabled database has a fundamental unit of storage that is considered to comprise of a dependent implementation process. A hybrid XML database is a database that can be regarded as either native XML database, or an XML enabled database depending on the nature and requirements of the application.

Transferring XML in an XML Enabled Document

XML-enabled databases are more applicable under a set-up where the main format for data exchange between the application and underlying databases is XML. For instance, a relational database may contain an XML document to provide data for a particular web service. The major attribute of the XML-enabled database storage tactic is the use of the data model that is different from XML and in most cases a relational data model(Maatuk, & Aljawarneh, 2015). The individual instance of the data model is mapped to an instance of the XML data model. For instance, the structure of the XML document required by the consuming application determines how a relational schema is mapped into a different XML schema. An XML-enabled database, the data exchange formats take the form of XML documents since they are not required to have any specific identity within the database. A practical situation can be identified in a situation where the XML is used to transfer data related to temperatures from a weather station to a database. Once the data from a specific document is transferred to the database, the original document can then be discarded (Alrefae, Cao & Pardede, 2018). For a reverse direction, if an XML document is requested as necessitated by the query; it can be constructed on-the-fly from the results that are retrieved after querying the underlying databases and then discarded after consumption by the client who had requested it. The reconstruction of the original document stored in the database cannot be guaranteed. For that reason, shredding of a document into an XML-enabled as a method of storage is highly discouraged. The XML-enabled systems can only be used to publish existing relational data without considering its source, into an XML.

The term publication or composition is used to refer to the process of data extraction from the database into properly constructed XML documents or fragments. Decomposition or shredding is the reversing process of data extraction from an XML document or fragment into a database (Lemahieu, Broucke, & Baesens, 2018). Two important matters require a careful consideration without any regards as to whether shredding or publication of the XML documents is to take place. The first issue relates to the possibility that an XML-enabled database does not contain XML implying that the XML document is completely considered as external to the database. The data that is already contained in the database should be used to construct either an XML document or a fragment. An XML document can also be used as a source of new data that is stored into the database. The second situation for consideration occurs when the XML schema matches with the database schema thus resulting to a different schema being required for each database schema. The software is normally included in an XML-enabled database to perform publishing and shredding functions between XML documents and the relational data (Cornish, 2017). A third party may provide the required software under a situation where it was not an already integrated type of a database. The software installed on XML database can be expected to handle the subclass documents as compared to all possible XML documents necessary for modelling data that is already found in the database.

Mapping of the XML-enabled database

Mapping of the database schema to an XML schema is necessary, especially when using the XML-enabled database (Brahmia, Grandi, & Bouaziz, 2016). Mappings can be categorized into two important forms which include the table-based mapping and object-relational mapping. The two types of mappings are bi-directional thus can be used to define the transfer of data to and from the database (Weinberg, Cherny, & SAP 2016). Table-based mapping requires that an XML document must have a similar structure to that of the relational database (Haw, & Ang, 2016). The similarity in structure implies that data can be grouped into rows and rows then grouped into tables. The XML document is seen as a set of serialised objects and is m...