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Chapter 15

Chapter 15. by David G. Messerschmitt. Databases. by David G. Messerschmitt. 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

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Chapter 15

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  1. 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.

  4. Two capabilities Application I Application II Sharing: two or more applications accessing the same databases Aggregation: accessing multiple databases Databases

  5. Relational table Table Employee Name Address Dept Record Field

  6. Database operations Employees Departments Each operation results in a new table, so they can be concatenated “PROJECT” “SELECT”

  7. Multiple tables “PROJECT” “SELECT”

  8. Record at a time processing Database Application logic (system programming language) SQL

  9. 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.

  10. Fields, columns, attributes • Entries are simple data types or compositions of those types • Integrity constraints Records, rows

  11. Object/table correspondence Class Class implementation Employee Name Address Dept Record-at-a-time program Object instance data Attribute

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

  13. 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

  14. 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.

  15. Markup languages by David G. Messerschmitt

  16. 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

  17. Example: HTML HEAD> <META NAME="GENERATOR" CONTENT="Adobe PageMill 2.0 Win"> <TITLE>David G. Messerschmitt Homepage</TITLE> </HEAD> <BODY ALINK="#c4124e" BACKGROUND="Images/background.jpg"> <H3>&nbsp;</H3> <BLOCKQUOTE> <H2><TABLE BORDER="5" CELLSPACING="2" CELLPADDING="0"> <TR> <TH> <P ALIGN=LEFT><IMG SRC="Images/Messer.gif" WIDTH="112" HEIGHT="168" ALIGN= "BOTTOM" NATURALSIZEFLAG="3"></TH></TR> </TABLE> </H2> <H2><BR> David G Messerschmitt</H2> <H3>Roger A. Strauch Professor of <A HREF="http://www.eecs.berkeley.edu/">Electrical Engineering and Computer Sciences</A></H3>

  18. Family lineage SGML XML HTML Emphasizes formatting and presentation of documents Emphasizes structure of documents Purpose- and industry-specific extensions

  19. 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

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