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Object-Relational Mapping in Database Systems Engineering

Understand how to persist and map objects to relational databases, address impedance mismatch, and evaluate ORM tools like Hibernate and Toplink.

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Object-Relational Mapping in Database Systems Engineering

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  1. CIS 764 Database Systems Engineering • L18.2 : Object Relational Mapping … • ….Object persistence http://www.cis.ksu.edu

  2. CIS 764 Database Systems Engineering Objects are transient .. they last as long as run environment is alive (as long as a middleware session) Object persistence is the automatic save/load of object state to some persistent storage form (e.g. persisting between sessions). Example storage: binary data files (e.g. Word doc) XML files (e.g. UML XMI) relational data base (using SQL) <<<< Object data base Note: first three save only the state, not the methods. http://www.idt.mdh.se/kurser/cd5130/msl/2006lp4/reports/drafts/object_persistence.pdf http://www.cis.ksu.edu

  3. CIS 764 Database Systems Engineering Object persistence there are two issues: the form (format) of persistent storage the mapping of scalar data values. (e.g. Java and Oracle data types are not identical). http://www.cis.ksu.edu

  4. CIS 764 Database Systems Engineering Objects torelational data base (using SQL) is Object-Relational-Mapping. It can go both ways: objects -> tables tables -> objects (you used this in ADF assignment) Which way do we want to go? http://www.cis.ksu.edu

  5. CIS 764 Database Systems Engineering Which way do we want to go? Ans1: Design at the conceptual level: ER conceptual domain model (class model) Ans2: Build web applications for existing tables. Ans2a: tuning the DB and sync the model http://www.cis.ksu.edu

  6. CIS 764 Database Systems Engineering Impedance mismatch … refers to the difference in concepts between object models and table model. There is (IMHO) a reasonable mapping of object concepts to tables; not so clear mapping backwards. See following for discussions of mismatch: http://c2.com/cgi/wiki?ObjectRelationalMapping http://en.wikipedia.org/wiki/Object-Relational_impedance_mismatch http://www.cis.ksu.edu

  7. CIS 764 Database Systems Engineering Impedance mismatch … some issues:   * single persistent object  may spans several  tables         * objects "ownership“ ↔ relational * Objects have "getters"; expensive to submit several queries for single row; use Value object w “putAll” , “getAll” methods. * RDBMSs are  faster on global queries;              object faster for small scope (single objects).      * inefficient to keep objects  synchronized with database http://www.cis.ksu.edu

  8. CIS 764 Database Systems Engineering One suggestion is to map to object database: not for 764 focus … inefficient for object persistence in 3 layer model not likely transition for existing DB applications. http://www.cis.ksu.edu

  9. CIS 764 Database Systems Engineering OR tools available for most language platforms and target DBMS: http://en.wikipedia.org/wiki/Object-relational_mapping http://en.wikipedia.org/wiki/List_of_object-relational_mapping_software http://www.cis.ksu.edu

  10. CIS 764 Database Systems Engineering Toplink  ( 1990 Smalltalk, ~ 1995 Java)  purchased by Oracle in 2002               objects and beans to DB or XML (targets multiple DBs)                integrated with JDeveloper; http://www.oracle.com/technology/products/ias/toplink/index.html http://en.wikipedia.org/wiki/TopLink … donated for open source Eclipse project, … used for Sun EJB3 reference implemenation …. You implicitly used it for ADF homework http://www.cis.ksu.edu

  11. CIS 764 Database Systems Engineering    JDO       Java Data Objects  (~2003)   http://java.sun.com/products/jdo/                   a standard interface-based Java model abstraction of persistence;                   applications are portable, and independent of the underlying database (provided there is a JDO mapping)                    can be used with POJO  or with EJB; uses a persistence manager class; but ... has not been a dominant technology http://www.cis.ksu.edu

  12. CIS 764 Database Systems Engineering   Hibernate   http://www.hibernate.org/    (~2004)   express queries in SQL extension (HQL) or native SQL  or with an object-oriented Criteria and Example API;          open source project ; entity manager for EJB3.0; generates a configuration file that defines the mapping key component of  JBoss  (http://www.jboss.com/products/index)           integrates with Eclipse   http://www.myeclipseide.com/ContentExpress-display-ceid-61.html the major ORM tool . (See also Gardner Hibernate slides) http://www.cis.ksu.edu

  13. CIS 764 Database Systems Engineering      NHibernate …. port of  the core   to the .NET Framework; Suspend2  http://www.suspend2.net/                    … Linux equivalent http://www.cis.ksu.edu

  14. CIS 764 Database Systems Engineering Ruby-on-Rails  http://www.rubyonrails.org/             a "full-stack"  framework for developing DB web applications;             follows the Model-View-Control pattern;            includes Active Record  persistence framework; an "agile programming" approach ... based on the Ruby language  http://www.ruby-lang.org/en/  (~1995) “Active Record” name comes from the pattern for object that wraps a DB row ( e.g. an entity ejb). See also Enterprise patterns <<<<<<<<<<<<<<<<<<<< http://www.martinfowler.com/eaaCatalog/index.html http://www.cis.ksu.edu

  15. CIS 764 Database Systems Engineering Django      http://www.djangoproject.com/     (~2005)                 a high-level Python Web DB framework                    includes ORM … configuration defined in Python code.                 Includes a sample app in the tutorial . http://www.cis.ksu.edu

  16. CIS 764 Database Systems Engineering end. http://www.cis.ksu.edu

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