February,2006 Advanced DB System Object Relational Model Prof: Dr Rahgozar Euhanna Ghadimi, Mostafa Keikha Discussion, Implementation

February,2006 Advanced DB System Foreword  “ Object databases will gain ground, but their share of the world ’ s data will still be very small. The big change will come from the relational databases as they extend their databases to support more object-oriented features. ” Martin Fowler, Oracle Press, 1999

February,2006 Advanced DB System outline  History of DB Models  Object-Relational Model  Base features  Concepts  Examples  Object Relation mapping (ORM)  “ Modern ” ORM Solutions  Conclusion

February,2006 Advanced DB System History of DB Models  1950 File Systems, Punched Cards  1960 Hierarchical (IMS IBM Mainframes)  1970 Network (CODASYL, IDMS)  1980 Relational (ORACLE, DB2, Sybase)  1990 Object-Oriented, Object-Relational (O2, ORACLE9i)

February,2006 Advanced DB System Relational Model  Emergence of data model  Data independence  High-level approach  Standardization  Built-in data types  Little abstraction  Separation between data and operations

February,2006 Advanced DB System Object-Oriented Model  Complex application datatypes  Object Abstraction  Encapsulation of behavior  High performance for specific application  No backwards compatibility  Closely tied to language and application

February,2006 Advanced DB System Object-Relational Model  Synthesis of two worlds  Upward compatibility  Robustness of mature systems  Legacy problems  Backward Compatibility

February,2006 Advanced DB System Main Features Relation is still the fundamental abstraction, with integration of OO features  Structured Types Non-atomic types  Methods Special operations can be defined for a type  References Pointers to tuples  SQL-99 includes many of the object-relational features to be described.

February,2006 Advanced DB System Structured Types - I  Attributes of relation schemas can be  Atomic  Relation schemas: Nested Relations

February,2006 Advanced DB System Structured Types - II 4NF1NF Nested

February,2006 Advanced DB System Structured Types  UDT – User Defined Type  A UDT can be the type of a table  A UDT can be the type of an attribute belonging to some table  A UDT can inherit from another UDT CREATE TYPE T AS ;

February,2006 Advanced DB System Nested Relations Example CREATE TYPE AddressType AS ( street CHAR(50), city CHAR(20) ); CREATE TYPE AddressTypeTable AS TABLE OF AddressType; CREATE TYPE StarType AS ( name CHAR(30), address AddressTypeTable ); CREATE TABLE MovieStar OF StarType;

February,2006 Advanced DB System Methods – SQL99  Special operations defined for a type  In SQL, implementation defined with Presistent Stored Modules (PSM) language METHOD m() RETURNS ;

February,2006 Advanced DB System Methods - Example CREATE TYPE AddressType AS ( street CHAR(50), city CHAR(20) ) METHOD houseNumber() RETURNS CHAR(10); CREATE METHOD houseNumber() RETURNS CHAR(10) FOR AddressType BEGIN … END;

February,2006 Advanced DB System References - I  Allow a tuple t refer to a tuple s rather than including s in t

February,2006 Advanced DB System References - II  If attribute A has a type that is a reference to a tuple in relation with schema R, we denote A as A(*R)  If A is a set of references, we denote A as A({*R})

February,2006 Advanced DB System References – SQL99 - I  A table which type is a UDT may have a reference column that serves as its “ ID ” In CREATE TABLE statement, add REF IS Where is either  SYSTEM_GENERATED : DBMS generates unique IDs  DERIVED : DBMS uses primary key of the relation for IDs

February,2006 Advanced DB System References – SQL99 – I - Example CREATE TYPE MovieType AS ( title CHAR(30), year INTEGER ); CREATE TABLE Movie OF MovieType ( REF IS movieID DERIVED, PRIMARY KEY (title, year) );

February,2006 Advanced DB System References – SQL99 - II Reference to a tuple of type T REF(T) Reference to tuples in relation R, where R is a table whose type is the UDT T REF(T) SCOPE R

February,2006 Advanced DB System References – SQL99 - II – Example CREATE TYPE StarType AS ( name CHAR(30), address AddressType, bestMovie REF(MovieType) SCOPE Movie ); NameAddressbestMovie Hamill streetcity Sunset Blvd LA

February,2006 Advanced DB System Object Relation mapping (ORM)  although OR DBs solve many problems, they are not so much practical.  Why?  ORM

February,2006 Advanced DB System What do RDBs do well?  Work with large amounts of data  Searching, sorting  Work with sets of data  Joining, aggregating  Sharing  Concurrency (Transactions)  Many applications  Integrity  Constraints  Transaction isolation

February,2006 Advanced DB System What do RDBs do badly?  Modeling  No polymorphism  Fine grained models are difficult  Business logic  Stored procedures (really they are sufficient?) Goal: Take advantage of those things that relational databases do well Without leaving the language of objects / classes Final goal :Do less work, Happy DBA

February,2006 Advanced DB System “ Modern ” ORM Solutions  Transparent Persistence  Persistent/transient instances  Automatic Dirty Checking  Transitive Persistence  Lazy Fetching  Outer Join Fetching  Runtime SQL Generation

February,2006 Advanced DB System Auction Object Model

February,2006 Advanced DB System Persistent Class  Default constructor  Get/set pairs  Collection property is an interface type  Identifier property public class AuctionItem { private Long _id; private Set _bids; private Bid _successfulBid private String _description; public Long getId() { return _id; } private void setId(Long id) { _id = id; } public String getDescription() { return _description; } public void setDescription(String desc) { _description=desc; } … }

February,2006 Advanced DB System XML Mapping  Readable metadata  Column / table mappings  Candidate key generation strategy  Collection metadata  Fetching strategies <set name= “ bids ” cascade= “ all ” lazy= “ true ” >

February,2006 Advanced DB System Dirty Checking  Retrieve an AuctionItem and change description Session session = sessionFactory.openSession(); Transaction tx = s.beginTransaction(); AuctionItem item = (AuctionItem) session.get(ActionItem.class, itemId); item.setDescription(newDescription); tx.commit(); session.close();

February,2006 Advanced DB System Transitive Persistence  Retrieve an AuctionItem and create a new persistent Bid Bid bid = new Bid(); bid.setAmount(bidAmount); Session session = sf.openSession(); Transaction tx = session.beginTransaction(); AuctionItem item = (AuctionItem) session.get(ActionItem.class, itemId); bid.setItem(item); item.getBids().add(bid); tx.commit(); session.close();

February,2006 Advanced DB System Detachment  Retrieve an AuctionItem and create a new persistent Bid Session session = sf.openSession(); Transaction tx = session.beginTransaction(); AuctionItem item = (AuctionItem) session.get(ActionItem.class, itemId); tx.commit(); session.close(); item.setDescription(newDescription); Session session2 = sf.openSession(); Transaction tx = session2.beginTransaction(); session2.update(item); tx.commit(); session2.close();

February,2006 Advanced DB System Optimizing Data Access  Eager (Outer Join) Fetching  Lazy Fetching  Batch Fetching

February,2006 Advanced DB System Outer Join Fetching AuctionItem item = (AuctionItem) s.get(ActionItem.class, itemId); SELECT … FROM AUCTION_ITEM ITEM LEFT OUTER JOIN BID BID1 ON BID1.ITEM_ID = ITEM.ITEM_ID LEFT OUTER JOIN BID BID2 ON BID2.BID_ID = ITEM.SUCCESSFUL_BID WHERE ITEM.ITEM_ID = ?

February,2006 Advanced DB System Lazy Fetching AuctionItem item = (AuctionItem) session.get(ActionItem.class, itemId); SELECT … FROM AUCTION_ITEM ITEM WHERE ITEM.ITEM_ID = ? Iterator iter = item.getBids().iterate(); SELECT … FROM BID BID WHERE BID.ITEM_ID = ? item.getSuccessfulBid().getAmount(); SELECT … FROM BID BID WHERE BID.BID_ID = ?

February,2006 Advanced DB System Data Access mechanism <many-to-one name= “ successfulBid ” outer-join= “ true ” column= “ SUCCESSFUL_BID_ID ” /> <set name= “ bids ” cascade= “ all ” Lazy= “ true ” >

February,2006 Advanced DB System Optimizing Data Access  Minimize row reads  Use lazy fetching N+1 Selects Problem (too many roundtrips)  Minimize database roundtrips  Use outer join fetching Cartesian Product Problem (huge result set)  (Much less important) Minimize column reads

February,2006 Advanced DB System Optimizing Data Access Solution: Runtime Fetch Strategies 1.Say what objects you need 2.Navigate the object graph

February,2006 Advanced DB System Possible options  Intermediate Query Language  “ Minimal ” OO concepts combine with of ANSI SQL  Native SQL Queries with OO methods (DQE)

February,2006 Advanced DB System Intermediate Query Language  Make SQL be object oriented  Classes and properties instead of tables and columns  Polymorphism  Associations  Much less shorter than SQL  Full support for relational operations  Inner/outer/full joins, cartesian products  Projection  Aggregation (max, avg) and grouping  Ordering  Subqueries  SQL function calls

February,2006 Advanced DB System Intermediate Query Language  IQL is a language for talking about “ sets of objects ”  It unifies relational operations with object models Simplest IQL Query: from AuctionItem i.e. get all the AuctionItems: List allAuctions =session.createQuery(“from AuctionItem”).list();

February,2006 Advanced DB System Intemediate Query Language More realistic example: select item from AuctionItem item join item.bids bid where item.description like ‘ hib% ’ and bid.amount > 100 i.e. get all the AuctionItem s with a Bid worth > 100 and description that begins with “ hib ”

February,2006 Advanced DB System Intermediate Query Language Projection: select item.description, bid.amount from AuctionItem item join item.bids bid where bid.amount > 100 order by bid.amount desc i.e. get the description and amount for all the AuctionItems with a Bid worth > 100

February,2006 Advanced DB System Intermediate Query Language Aggregation: select max(bid.amount), count(bid) from AuctionItem item left join item.bids bid group by item.type order by max(bid.amount)

February,2006 Advanced DB System Intermediate Query Language Runtime fetch strategies: AuctionItem item = session.createQuery( … ).uniqueResult(); //associations already fetched item.getBids().iterator(); item.getSuccessfulBid().getAmount(); from AuctionItem item left join fetch item.bids join fetch item.successfulBid where item.id = 12

February,2006 Advanced DB System Criteria Queries List auctionItems = session.createCriteria(AuctionItem.class).setFetchMode( “ bids ”, FetchMode.EAGER).add( Expression.like( “ description ”, description) ).createCriteria( “ successfulBid ” ).add( Expression.gt( “ amount ”, minAmount) ).list(); Equivalent IQL: from AuctionItem item left join fetch item.bids where item.description like :description and item.successfulbid.amount > :minAmount

February,2006 Advanced DB System Example Queries AuctionItem item = new AuctionItem(); item.setDescription( “ hib ” ); Bid bid = new Bid(); bid.setAmount(1.0); List auctionItems = session.createCriteria(AuctionItem.class).add( Example.create(item).enableLike(MatchMode.START) ).createCriteria( “ bids ” ).add( Example.create(bid) ).list(); Equivalent IQL: from AuctionItem item join item.bids bid where item.description like ‘ hib% ’ and bid.amount > 1.0

February,2006 Advanced DB System Conclusion  whether Object-Relation mapping can be successful forever?  they are continue until they can convert objects to relation.

February,2006 Advanced DB System References [1]. Mapping Objects to Relational Databases: O/R Mapping in Detail, Scott W.ambler July [2] A Relational Model of Data for Large Shared Data Banks, E. F. Codd, [3] Achievement and weaknesses of object oriented databases, Sikha Bagui, Department of Computer Science, University of West Florida, U.S.A, Published by ETH Zurich,2003. [4] On type systems for object oriented database programming language, Yuri Leontiev, M. Tammer Ozsa, Duane Szafron, ACM Computing Surveys,2002 [5] object/Relational Access Layers, a roadmap, Missing Links and More Patterns, wolfgang keller, 3rd European conference of pattern languages of programming and computing [6] DB2's Object-Relational Highlights ibm.com/developerworks/db2/library/techarticle/zeidenstein/0108zeidenstein.html [7]Simple Strategies for Complex Data: Oracle9i Object-Relational Technology