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Object-Oriented Databases
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Record-oriented data models are powerful when applied to
traditional database applications
However in a relational model,
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data is organized as a flat tuple
the schema are relatively static
relationships among data must be explicitly specified as integrity constraints
traditional models lack functionality in supporting advanced
database applications
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CAD/CAM and CIM, Image and graphics, Geographic and scientific,
multimedia, documents, etc.
Characteristics and requirements
complex structures of objects
– new data types for unstructured data (e.g. BLOB)
– reactive(endless) activities
– long-duration (open-ended) activities
– collaborating (cooperative) activities
OO Data models and OO database systems are proposed to address
these requirements
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Systems and Interfaces
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experimental prototypes
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commercial OODB Systems
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ORION (MCC), OpenOODB (Texas Instruments), IRIS(HP),
ODE(ATT Bell Labs), ENCORE/ObServer (Brown), ...
GEMSTONE/OPAL (Servio Logic), O2 (O2 Technology),
ObjectStore (Object Design), ...
OO Shells or Interfaces
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Paradox, Access, ..
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OO Concepts
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Concepts are adopted from OO programming languages
Object
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is an instance of abstract data type (ADT)
hides the internal data structure (information hiding)
can be accessed and manipulated by the application using a set of operations
specific to the ADT (encapsulations)
Objects in programming languages are transient
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Objects in DB are persistent
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collections of objects, either implicitly or explicitly specified
contain associated methods, which are algorithms specifying how the objects in
that class are to be manipulated
Hierarchy
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they are persistent and can be shared by a number of programs
Class
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exist only during program execution
imposes an acyclic graph structure on the set of classes
an OODBS supports an interface to one or more OO programming
languages providing persistent and shared object capabilities while
treating transient and persistent objects uniformly
there is no single OO data model. However, there is a set of concepts
that an OO data model and OODB must support
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Example Hierarchies
Documents
Museums
Image HTML Word Raw text
Mac
IBM PC
Art
Smithsonian
Science
Natural History
Metropolitan
New York
Baltimore
Aquarium
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OO Concepts (continued)
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Object Identifier: a unique and immutable system-wide id (not true with
relational data model)
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Object structure can be of arbitrary complexity in order to contain all significant
information (in relational the information is scattered over many relations)
instance variables
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Object internal structure includes the specification of instance variables that hold its
state.
instance variables could be complex objects themselves
type constructors
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OODB maintains a direct correspondence between real-world and database
objects
complex object structures can be constructed by recursively applying a set of basic
type constructors such as tuple, set, list, and bag
encapsulation
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complete encapsulation: only a specific set of predefined operations or functions
can be applied on a particular object
 assumes object independence
 does not permit explicit specification of relationships between objects
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Objects
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An object is defined as a pair: (id, values)
Example:
declare b2
values [author = John Smith,
url = http://www.somewhere.com/
date_created = (15, Jan, 1999)
date_last_modified = (25, Jan, 1999)
Types
 Record
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type, Set type, List type
Examples:
[author: string;
url: urltype;
date_created: datetype;
date_last_modified: datetype]
[address: string;
director: string;
special_exhibits: {string};
affiliated_museums: {Oid_set}]
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Operations on Objects
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Each operation has two parts
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(1) signature or interface: specifies name and arguments of
the operation (externally visible)
(2) method or body: specifies the implementation of the
operation (externally invisible)
Operations can be invoked by passing a message to
an object
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objects' internal structure and operations' implementation
can be changed without affecting the programs that access
them
This provides encapsulation
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Types, Class Hierarchy and Inheritance
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Object type: set of allowable values
Object class: collection of objects meaningful in an application
New types and classes can be specified based on existing
ones
Inheritance: new types and classes inherit much of the
structure and operations from the type/class they are derived
incremental development of system data type is supported
ability to reuse existing type definitions and implementations
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Object Definition Language (ODL)
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Simple language within which objects and interfaces can be
defined
ODL provides a formal syntax to access the signatures of
the objects so that external programs wishing to
access/manipulate the object using the methods provided
by the object
Example:
interface html:documents
(extent html_documents
keys url: persistent
{<properties>
<operations>}
);
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Object Query Language (OQL)
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If Q is expressed in SQL, then Q is also a valid OQL query
SQL queries can access only flat relational tables
In contrast, objects may have a nested structure, as well as
include fields that contain collection types - sets, lists, ..
OQL facilitates access to such data types
Examples:
select
from
where
struct(field1:x.url, field2:x.link)
Word x
x.author = “John Smith”
select
from
y.author
(select x.link
from Word x
where x.author = “John Smith”) y
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Object-Relational Systems
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Relational databases have proved very useful in querying
flat data
Is it possible to extend the relational model to handle
complex data?
Yes, The resulting paradigm is object-relational
Example:
 Consider
a bank relation schema
(Fname, Lname, AccType, Trans, Amount, Day)
and a crime relation schema
(SSN, FirstName, LastName, Conviction, Day)
 Suppose we extended both these schemes to include images as
follows:
(Fname, Lname, AccType, Trans, Amount, Day, PIC)
(SSN, FirstName, LastName, Conviction, Day, PIC)
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Example Continued
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If a customer reports that her ATM card was stolen and she
did not make the last withdrawal
To verify, the bank needs to look at the surveillance image
and see if it is that of the customer
If not, the next logical step for the police to perform is to
attempt check if there is a match between the image in
surveillance record with any image in the crime database
This needs execution of the query
 “Select
all tuples in the crime relation that match the image in
customer record”
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SQL cannot support such query directly because the
comparison operator “match” is not supported by a
relational database
An object db language cannot be used either because the
data is not stored in an object-oriented db
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Object-Relational Scheme
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Object relational scheme:
(A1:T1, … An:Tn)
where Ai’s are attribute names and Ti’s are objects
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Example:
(Fname:str, Lname:str, AccType:int, Trans:tt, Amount:real,
Day:date, PIC:image)
(SSN:ssntype, FirstName:str, LastName:str, Conviction:str,
Day:date, PIC:image)
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object conditions
 match(image1,image2)
> 0.7;
 match(image1,image2) > match(image3,image2);
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Query
select
from
where
Fname,Lname
Crime C, Bank B
match(B.image1,C.PIC) > 0.9
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Commercial Object-relational Systems
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Informix
 offers
a variety of datablades for image db, face recognition,
audio data handling, document processing, video processing,
spatial db
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DB2
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similar features called extenders
Oracle
Sybase
Uni-Sql and Ominiscience employ O-R technology
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