David G. Messerschmitt

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Chapter 15

• by
• David G. Messerschmitt

2
Databases

• by
• David G. Messerschmitt

3
Databases

• Treat data as a separate asset
• May be shared by multiple applications
• Provide protection and integrity features
  appropriate to mission-critical data
• Access control
• Integrity constraints
• Persistence
• etc.

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Two capabilities
Application I
Application II
Sharing two or more applications accessing the
same databases
Aggregation accessing multiple databases
Databases
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Relational table
Table
Employee
Name
Address
Dept
Record
Field
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Database operations
Employees
Departments
Each operation results in a new table, so they
can be concatenated
PROJECT
SELECT
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Multiple tables
PROJECT
SELECT
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Record at a time processing
Database
Application logic (system programming language)
SQL
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SQL interface

• Presents single abstract interface to the
  application logic
• Standardized, not vendor specific
• Stored procedures and extensions violate this
• Encapsulates various internal details
• Data partitioning and replication
• Host mapping
• File representation
• etc.

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Fields, columns, attributes

• Entries are simple data types or compositions of
  those types
• Integrity constraints

Records, rows
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Object/table correspondence
Class
Class implementation
Employee
Name
Address
Dept
Record-at-a-time program
Object instance data
Attribute
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Object attributes

• Rows can be considered object instances with the
  same attributes
• Restriction to simple data types
• No encapsulated state
• No methods

Object instances
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Object-relational database

• A column can store object instances of a given
  class rather than data of a given simple or
  compound data type
• Because of the table structure, SQL can be
  extended to this case
• Standard SQL queries can be extended to methods
  returning simple data types
• Many other good ideas

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Benefits of ORDBMS

• Extension manage arbitrarily complex data types
• Migration preserve and extend existing databases
• Preserve SQL interface
• OR extensions in latest standard
• All the benefits/experience of earlier databases
• Access control, data integrity, persistence, etc.
• Killer app Behind Web/CGI
• Images, video, audio, animation, applets, etc.

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Markup languages

• by
• David G. Messerschmitt

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Definition

• A markup language describes the structure of a
  document
• Based on tags
• Tags denote structural elements like sections,
  subsections, figures, etc
• Internationally standardized, so application
  independent

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Example HTML

• HEADgt
• ltMETA NAME"GENERATOR" CONTENT"Adobe PageMill
  2.0 Win"gt
• ltTITLEgtDavid G. Messerschmitt Homepagelt/TITLEgt
• lt/HEADgt
• ltBODY ALINK"c4124e" BACKGROUND"Images/backgroun
  d.jpg"gt
• ltH3gtnbsplt/H3gt
• ltBLOCKQUOTEgt
• ltH2gtltTABLE BORDER"5" CELLSPACING"2"
  CELLPADDING"0"gt
• ltTRgt
• ltTHgt ltP ALIGNLEFTgtltIMG SRC"Images/Messer.gif"
  WIDTH"112" HEIGHT"168" ALIGN
• "BOTTOM" NATURALSIZEFLAG"3"gtlt/THgtlt/TRgt
• lt/TABLEgt
• lt/H2gt
• ltH2gtltBRgt
• David G Messerschmittlt/H2gt
• ltH3gtRoger A. Strauch Professor of ltA
  HREF"http//www.eecs.berkeley.edu/"gtElectrical
• Engineering and Computer Scienceslt/Agtlt/H3gt

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Family lineage
SGML
XML
HTML
Emphasizes formatting and presentation
of documents
Emphasizes structure of documents
Purpose- and industry-specific extensions
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Data sharing among applications

• Options include
• Messages with defined formats
• Documents (eg. XML)
• Shared databases
• Remote method invocation middleware
• The first two are the most practical for
  inter-enterprise applications