Understanding Networked Applications: A First Course Chapter 15 by David G. Messerschmitt

Understanding Networked Applications: A First Course Databases by David G. Messerschmitt

Understanding Networked Applications A First Course 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.

Understanding Networked Applications A First Course 4 Databases Application IApplication II Aggregation: accessing multiple databases Sharing: two or more applications accessing the same databases Two capabilities

Understanding Networked Applications A First Course 5 Employee NameAddressDept Record Field Table Relational table

Understanding Networked Applications A First Course 6 “PROJECT”“SELECT” Departments Employees Database operations Each operation results in a new table, so they can be concatenated

Understanding Networked Applications A First Course 7 “PROJECT”“SELECT” Multiple tables

Understanding Networked Applications A First Course 8 Database Application logic (system programming language) SQL Record at a time processing

Understanding Networked Applications A First Course 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.

Understanding Networked Applications A First Course 10 Fields, columns, attributes Records, rows Entries are simple data types or compositions of those types Integrity constraints

Understanding Networked Applications A First Course 11 Employee NameAddressDept Object instance data Attribute Class Record-at-a-time program Class implementation Object/table correspondence

Understanding Networked Applications A First Course 12 Object attributes Object instances Rows can be considered object instances with the same attributes Restriction to simple data types No encapsulated state No methods

Understanding Networked Applications A First Course 13 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 Object-relational database

Understanding Networked Applications A First Course 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.

Understanding Networked Applications: A First Course Markup languages by David G. Messerschmitt

Understanding Networked Applications A First Course 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

Understanding Networked Applications A First Course 17 Example: HTML HEAD> David G. Messerschmitt Homepage <IMG SRC="Images/Messer.gif" WIDTH="112" HEIGHT="168" ALIGN= "BOTTOM" NATURALSIZEFLAG="3"> David G Messerschmitt Roger A. Strauch Professor of Electrical Engineering and Computer Sciences

Understanding Networked Applications A First Course 18 Family lineage SGML HTML XML Emphasizes formatting and presentation of documents Emphasizes structure of documents Purpose- and industry-specific extensions

Understanding Networked Applications A First Course 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