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February,2006 Advanced DB System Object Relational Model Prof: Dr Rahgozar Euhanna Ghadimi, Mostafa Keikha Discussion, Implementation Slide 2 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 Slide 3 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 Slide 4 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) Slide 5 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 Slide 6 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 Slide 7 February,2006 Advanced DB System Object-Relational Model Synthesis of two worlds Upward compatibility Robustness of mature systems Legacy problems Backward Compatibility Slide 8 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. Slide 9 February,2006 Advanced DB System Structured Types - I Attributes of relation schemas can be Atomic Relation schemas: Nested Relations Slide 10 February,2006 Advanced DB System Structured Types - II 4NF1NF Nested Slide 11 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 ; Slide 12 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; Slide 13 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 ; Slide 14 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; Slide 15 February,2006 Advanced DB System References - I Allow a tuple t refer to a tuple s rather than including s in t Slide 16 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}) Slide 17 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 Slide 18 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) ); Slide 19 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 Slide 20 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 Slide 21 February,2006 Advanced DB System Object Relation mapping (ORM) although OR DBs solve many problems, they are not so much practical. Why? ORM Slide 22 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 Slide 23 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 Slide 24 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 Slide 25 February,2006 Advanced DB System Auction Object Model Slide 26 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; } } Slide 27 February,2006 Advanced DB System XML Mapping Readable metadata Column / table mappings Candidate key generation strategy Collection metadata Fetching strategiesSlide 28 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(); Slide 29 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(); Slide 30 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(); Slide 31 February,2006 Advanced DB System Optimizing Data Access Eager (Outer Join) Fetching Lazy Fetching Batch Fetching Slide 32 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 = ? Slide 33 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 = ? Slide 34 February,2006 Advanced DB System Data Access mechanism Slide 35 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 Slide 36 February,2006 Advanced DB System Optimizing Data Access Solution: Runtime Fetch Strategies 1.Say what objects you need 2.Navigate the object graph Slide 37 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) Slide 38 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 Slide 39 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(); Slide 40 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 Slide 41 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 Slide 42 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) Slide 43 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 Slide 44 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 Slide 45 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 Slide 46 February,2006 Advanced DB System Conclusion whether Object-Relation mapping can be successful forever? they are continue until they can convert objects to relation. Slide 47 February,2006 Advanced DB System References [1]. Mapping Objects to Relational Databases: O/R Mapping in Detail, Scott W.ambler July 4 2005 [2] A Relational Model of Data for Large Shared Data Banks, E. F. Codd, 1970. [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 http://www- 106.ibm.com/developerworks/db2/library/techarticle/zeidenstein/0108zeidenstein.html [7]Simple Strategies for Complex Data: Oracle9i Object-Relational Technology http://www.oracle.com/technology/product/oracle9i/pdf/simple_strat_for_complex_rel2.pdf