1
What is this describing?

• The columns in the tables cover a year at ten
  day intervals. The decans are placed in the order
  in which they arise and in the next column, the
  second decan becomes the first and so on.
• Tables to help make these computations have been
  found on the _____________

inside of coffin lids
2
So what IS a database?

• Some sort of permanency
• Allows data to be extracted (easily)
• Can allow data to be appended
• Can allow data to be inserted, deleted or
  modified
• more difficult pre-computer age
• Contains data!

3
Lets name some databases.

• I will go first
• ORACLE !

4
Ways of managing modern databases

• Flavours of Database Management System (DBMS)
  include
• Relational
• Object-Relational
• Hierarchical Databases
• Network Databases
• Object Oriented
• But whatever the dbms, they are all about mapping
  logical constructs to physical ons and offs
  recorded permanently, normally on a HDD.

5
Common building blocks

• BIT
• 0 or 1, true or false.
• BYTE 8 bits
• 1010 1010 ascii J
• FIELD or Column
• SURNAME (eg Jones)
• Record or Row
• Several Fields (Deptno, Desc, Loc)
• File or Table
• Several Records
• Database
• Several Files

6
Issues of Access

• Sequential
• with n records, n/2 probes required to find data
• when n is large, very inefficient
• So willingly spend time storing records with
  retrieval in mind
• Order the data itself
• Create indexes

7
From access method to DBMS

• Whatever the dbms, core physical decisions are
  being taken
• It is all about mapping from the logical to the
  physical disk storage in the most efficient way.
• This will differ, depending upon what you are
  trying to do
• query intensive
• data quantities
• data complexity
• user volumes
• architecture available

8
DBMS - why the differences?

• Driven by both technology and different needs
• Hierarchical developed initially for product
  assemblies
• Network DB driven by need for inventory control
  (one supplier-several products AND products
  supplied by several suppliers)
• RDBMS the need to keep records
• OODBMS Complex business objects, CAD

9
RDBMS - some weaknesses

• Translation needed from real world to relational
• one argument for the move to OO paradigm
• Assumes all rows will contain the same attributes
• can lead to masses of virtual empty spaces which
  slows recovery
• Constraint checking is a hefty overhead
• should some of this be handled by the UI?
• Recent impact of middle-tier as a place for rules
• SQL is non-procedural and was specifically
  designed to be approachable to non-programmers
• hence PL/SQL as a work-around
• Is all data SET-orientated?

10
Hierarchical Databases

• Common in the mainframe environment
• One of the oldest DBMS
• IMS still performing strongly
• Organised like the branches of a tree
• single parent can have many children, but cant
  be related to other parents
• record searches and updates can be rapid, as the
  structure is pre-defined. They always start from
  the top.

11
Hierarchical cont...
Salesman
Buyer A
Buyer B
Buyer C
Product 1
Product 5
Product 4
12
Object DBMS

• Industry Standards set by ODMG
• Object Database management group
• www.odmg.org
• ODBMS is defined (by them) as
• ..a DBMS that integrates database capabilities
  with object-oriented programming capabilities
• Major components include
• Core Object Model
• ODL - for specifying objeccts
• OQL - for querying (very close to SQL92)
• Binding to C,Smalltalk or Java

13
Common aspects of ODBMS

• Object (always has an OID)
• Objects are of a type
• Types describe a common set of properties
  (states) and of behaviour (methods)
• State of Object defined by the values of
  properties or of relationships with other objects
• Database has a Object Manager layer between
  objects and permanent storage. Schema defined in
  ODL.
• Much more info at the OODBMD manifesto site
• http//www-2.cs.cmu.edu/People/clamen/OODBMS/Manif
  esto/htManifesto/Manifesto.html

14
ODBMS is ideal for

• Complex modelling environments because objects
  allow high levels of abstraction
• Non record-focused applications
• CAD
• Multimedia
• Reusability focused, modular systems

15
ODBMS - where are they?

• Performance, in terms of storing and retrieving
  data, can be poor
• RDBMS have a stranglehold on the commercial
  database marketplace
• The provision of a halfway house
  Object-Relational model
• Whilst the Assembler programmer predicts exactly,
  the architect of complex components is too far
  removed from the disk access to be able to design
  efficiently ?
• http//www.dbazine.com/pascal10.html

16
ODBMS - where are they?

• Some examples which prove OO is very much still
  alive
• OBJECTIVITY http//www.objectivity.com/
• Versant http//www.versant.com/
• ObjectDB http//www.objectdb.com/

17
XML

• "XML is a human-readable, machine-understandable,
  general syntax for describing hierarchical data,
  applicable to a wide range of applications,
  databases, e-commerce, Java, web development,
  searching, and so on. "
• Oracle OTN website, my italics
• Building blocks are Tags, Elements and
  attributes
• Separates Data from validity checking and from
  presentation
• by using DTD or Schemas to validate, and
  stylesheets to present

18
Native XML

• A native XML database...
• Defines a (logical) model for an XML document --
  as opposed to the data in that document -- and
  stores and retrieves documents according to that
  model.
• Has an XML document as its fundamental unit of
  (logical) storage, just as a relational database
  has a row in a table as its fundamental unit of
  (logical) storage.
• Is not required to have any particular underlying
  physical storage model. For example, it can be
  built on a relational, hierarchical, or
  object-oriented database, or use a proprietary
  storage format such as indexed, compressed files.
  

19
Issues with XML in RDBMS

• Paradigm conflict
• Hierarchical V Relational
• XML is not designed to be queriable.
• Xpath not as powerful as SQL?
• Whole new syntax to learn
• XML is not normalised
• ISO SQL does not lend itself to generating XML
  output

20
How to store XML in RDBMS

• Assuming XML inbound, do you
• break it up and store it in relational tables
• store the document as a CLOB (Character Large
  Object datatype)
• shred and store in a structured way, applying DTD
  or Schema rules?
• Depends how it will be used
• part of an existing rdbmd-based system which
  allows users to do ad hoc SQL queries
• just to forward on, as XML, to other users but
  seldom queried
• Held for use by XPath conversant users
• heavily CRUDed
• As permanence for Web-based Distributed
  Authoring and Versioning (DAV). Extensions to
  HTTP which allows users to collaboratively edit
  and manage files on remote web servers.

21
The future?

• Oracle Vs DB2 and SQL Server?
• In memory databases
• http//www.timesten.com/products/dataserver.html
• Post relational
• http//www.intersystems.com/cache/
• Shared processing models (grid)