Fall CIS 764 Database Systems Engineering L11: Object Relational Mapping … (a) ORM, Object persistence (b) Pets sequence models

Fall 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.

Fall 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).

Fall CIS 764 Database Systems Engineering Objects to relational data base (using SQL) is Object-Relational-Mapping. It can go both ways: objects -> tables tables -> objects (you used this in ADF assignment)

Fall CIS 764 Database Systems Engineering

Fall CIS 764 Database Systems Engineering

Fall CIS 764 Database Systems Engineering Which way do we want to go?

Fall 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.

Fall 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:

Fall 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. * RDBMSs are faster on global queries; object faster for small scope (single objects). * inefficient to keep objects synchronized with database

Fall 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.

Fall CIS 764 Database Systems Engineering OR tools available for most language platforms and target DBMS:

Fall CIS 764 Database Systems Engineering OR tools use w attributes in objects w configuration files w development wizards ( JDev)

Fall CIS 764 Database Systems Engineering Toplink ( ~ 1995 ??) purchased by Oracle in 2002 objects and beans to DB or XML (targets multiple DBs) integrated with JDeveloper; … donated for open source Eclipse project, … used for Sun EJB3 reference implemenation …. You implicitly used it for ADF homework

Fall CIS 764 Database Systems Engineering JDO Java Data Objects (~2003) 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

Fall CIS 764 Database Systems Engineering Hibernate (~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 ( integrates with Eclipse the major ORM tool.

Fall CIS 764 Database Systems Engineering NHibernate …. port of the core to the.NET Framework; Suspend2 … Linux equivalenthttp://

Fall CIS 764 Database Systems Engineering Ruby-on-Rails a "full-stack" framework for developing DB web applications; follows the Model-View-Control pattern; includes Active Record persistence framework; ttp:// an "agile programming" approach... based on the Ruby language (~1995) “Active Record” name comes from the pattern for object that wraps a DB row ( e.g. an entity ejb). See also Enterprise patterns <<<<<<<<<<<<<<<<<<<<

Fall CIS 764 Database Systems Engineering Django (~2005) a high-level Python Web DB framework includes ORM … configuration defined in Python code. Includes a sample app in the tutorial.

Fall CIS 764 Database Systems Engineering … many others. end.