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Object Databases

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Title: Object Databases


1
Object Databases
  • ???
  • OCIT
  • pychang_at_ocit.edu.tw

2
Reference
  • 1.Object-Relational DBMSstracking the next
    great wave by Michael. StoneBraker Paul.
    Brown,1999
  • 2.Object Databases An ODMG Approach by Richard
    Cooper,1997
  • 3.Fundation for Object/Relational Databases the
    third Manifesto, by C. J. Date, 1998

3
Chapter 1
  • Developments in database technology

4
What is a database system?
  • A DBMS is a coordinated package of software which
    permits large amount of structured data to be
    managed.

5
Facilities of a DBMS
  • Application generality. The DBMS will be able to
    handle data from many different application areas
    equally easily.
  • Efficient data access. The data will be stored in
    such a way that it can be accessed as quickly as
    possible.
  • Security. There will be privacy mechanisms
    securing the data against unauthorized access and
    misuse.
  • Data consistency Any changes made to the data
    will be organized in such a way that the database
    always remains consistent, i.e. no changes will
    be allowed to violate the organization imposed on
    the data by the database designer.

6
Facilities of a DBMS
  • Resilience. Hardware or software failures while
    the database is running are never allowed to make
    the database inconsistent - at most a few of the
    most recent changes will be lost if the system
    crashes.
  • Concurrency control. Many users can access the
    database at the same time without interfering
    with each others work.
  • Multiple views. There will be a facility for
    providing apparently different or more focused
    representations to different kinds of user.
  • Integrity. There may be the facility for imposing
    integrity constraints which limit the values
    which the database can take - thus maintaining
    the meaning of the information stored
  • Distribution. It may be possible for the DBMS to
    handle data which is distributed across more than
    one computer joined in a local network or even
    across a number of sites joined in a wider
    network.

7
Facilities of a DBMS
  • User interfaces. Appropriate user interfaces will
    be provided to allow databases to be designed and
    used by a wide variety of users. Among these will
    be
  • Parametric interfaces. Eg. Automated teller
    machines (ATMs) provide the most prevalent
    example of this kind of interface.
  • Ad hoc querying. The DBMS will provide a general
    purpose query language which gives users a fairly
    simple textual method for specifying the database
    structure updates to data and retrievals of data
    from the database.
  • Graphical interfaces. In order to simplify the
    interaction, there are a variety of emerging
    interface styles including node-and-arc graphs to
    represent the data structure
  • Programming interfaces.
  • Administrative interfaces.

8
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9
Logical data model
  • A data model is a set of constructs for
    describing data
  • The logical data model describes the structure
    data at the conceptual layer.
  • To create a database, its structure must be
    specified using the modeling constructs
    available. Such a specification is called a
    schema.

10
Transaction
  • A transaction consists of one or more changes to
    the database which take the database which take
    the database from one consistent state to
    another.
  • Properties of transaction
  • Atomicity. If a transaction is made up of a
    number of component updates, then every update
    must take effect or none of them should. The sum
    of money must not be debited without being
    credited or vice versa.
  • Consistency. The total effect of all of the
    components of the transaction must take the
    database from one consistent state to another.
    The total sum of money represented in the
    database must remain unchanged.
  • Isolation. Each transaction must not affect the
    smooth and correct running of any other
    transaction. Thus no two transactions are allowed
    to try to change the same account at the same
    time, for fear of corrupting each other.
  • Durability. After the transaction has
    successfully completed, nothing will permit the
    changes made to be lost - not even a system crash

11
Record-based DMBS
  • Network DBMS
  • Relational DBMS

12
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13
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14
New applications areas
  • CAD (computer aided design) CAE(computer aided
    engineering) CIM(computer integrated
    manufacturing)
  • CASE(computer aided software emgineering)
  • OIS(Office information system)
  • GIS(geographic information system)
  • WWW

15
Shortcomings of record-based DBMS
  • No direct support for
  • Hierarchies (part-of or is-a).
  • Advanced data types (spatial, multimedia).

16
ER model for relational database
17
EER involves inheritance
18
Derived data type TAXIS
  • PERSON_CLASS PERSON with
  • keys person_id (name, address)
  • characteristics name PERSON_NAME
  • address
    ADDRESS_VALUE
  • phone
    PHONE_VALUE
  • attribute_properties age AGE_VALUE
  • sex
    SEX_VALUE
  • end

19
Object Databases
  • Motivation to overcome weaknesses of relational
    approach
  • Richer data models.
  • Closer integration with programming languages.

20
Kinds of object database
  • Object relational (Oracle, DB2, PostgreSQL).
  • Programming language centred (Objectivity,
    FastObjects, Versant, ObjectStore).

21
Object Database Standards
  • SQL-99(SQL-3)
  • Mainstream SQL standard.
  • Oracle, DB2, Informix.
  • Object data management group (ODMG)
  • Outgoing mainstream object database standard.
  • Objectivity, FastObjects, Versant.
  • Java data objects (JDO)
  • Java-specific object-based database access.
  • Poet, Versant, ObjectStore, SolarMetric,

22
A Matrix for classifying database application
23
Quadrant1simple data without queries
  • cases text editor, VOD (video on demand)
  • Database simple file system

24
Quadrant2simple data with queries
  • database relational database
  • standard SQL-99

25
Quadrant2simple data with queries
  • Create table dept (
  • dname varchar(20,
  • budget float,
  • floor int)
  • create table emp (
  • name varchar (30),
  • startdate date,
  • salary float,
  • dept varchar(20))
  • Find the names of employees with an employment
    start date after 1980 and who earn more than
    40,000
  • Select name from emp where startdategt
    1980-12-31 and salary gt 40000
  • Find the names of employees who work on the 1st
    floor
  • Select name from emp where dept in
  • (select dname from dept where floor1)
  • Find the average salary of employees in the
    marketing department.
  • Select average(salary) from emp where
    deptmarketing

26
Quadrant2simple data with queries
  • Comments
  • Client tool Client tool (i.e. 4GL) to set up
    forms for data entry and display is required.
  • Performance transaction mechanism two-phase
    locking write-ahead log reduces performance.
  • Security/architecture
  • Market crowded

27
Quadrant3complex data without queries
  • database object-oriented database
  • standard ODMG, JDO

28
Quadrant3complex data without queries
create table emp ( name varchar (30),
space polygon, adjacency set-of
(empolyee))
create table floors ( number int, asf
swiss_cheese_polygon)
  • Objective arrange employees onto floors

main() read all employees read all
floors compact() write all
employees
main() compact()
29
Quadrant3complex data without queries
  • Comments
  • Query language is not required.
  • Client tools O-venders are expected to support
    many functions like compact().
  • Performance persistent object will slow down
    performance. The user wishes to run no more than,
    say, 10 shower than the nonpersistent case.
  • Security/architecture
  • Market ltlt relational DB.

30
Quadrant4complex data with queries
  • database object-relational database (ORDB)
  • standard SQL-99

31
Quadrant4complex data with queries
  • Example
  • The state of California Department of Water
    Resource (DWR) manages most of the waterways and
    irrigation canals in California, as well as a
    collection of aqueducts. To document their
    facilities, DWR maintains a library of 35-mm
    slides. Over time this library has grown to
    500,000 slides and accessed many times a day by
    DWR employees and others.
  • Problem clients usually requests a picture by
    content, ex. sunset. But it is difficult to
    find slides by content.

32
Quadrant4complex data with queries
  • Create table slides (
  • id int,
  • date date,
  • caption document,
  • picture photo_CD_image)
  • Create table landmarks (
  • name varchar(30),
  • location point)
  • Find the sunset picture taken within 20 miles of
    Sacramento
  • Select id from slides P, landmarks L, landmarks S
  • where sunset (P.picture) and contains
    (P.caption, L. name) and
  • L.location S.location and S.nameSacramento

33
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34
Quadrant4complex data with queries
  • Comments
  • Query language that allows user-defined functions
    and operations (SQL-99).
  • Client tools Standard 4GLs are useless. Advanced
    client tools are required. Ex. The case of DWR
    requires Zoom in/out user tool.
  • Performance user-defined function might
    time-consuming. Query optimizer is required. Ex
  • where sunset(image) and date lt 1985-01-01
  • Security/Architecture client-server
  • Market
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