1. © 2002 by Prentice Hall 1 David M. Kroenke Database Processing Eighth Edition Chapter 14 Networks, Multi-Tier Architectures, and XML

2. © 2002 by Prentice Hall 2 Networks A network is a collection of computers that communicate with one another using standard sets of rules, called protocols Common Network Environments: –Internet –Intranet –Wireless Network Access

3. © 2002 by Prentice Hall 3 The Internet Internet - a publicly accessible network of networks spanning the globe Uses communications protocol called Transmission Control Program/Internet Protocol (TCP/IP)

4. © 2002 by Prentice Hall 4 Key Dates for the Internet The Internet was born in the 1960’s by the US armed services and was called ARPANET HTTP: HyperText Transfer Protocol (used to create Web Pages) was created in 1989 by CERN –Key HTTP characteristics: Request-based (waits for user action) Stateless (does not sequence or remember activities)

5. © 2002 by Prentice Hall 5 HTTP: Stateless Property In applications development, you may often wish to save the application state. Several Internet tools exist to help accomplish this: –Microsoft Internet Information Server (IIS) –Microsoft Active Server Pages (ASP) –Java Servlets with Java ServerPages (JSP)

6. © 2002 by Prentice Hall 6 The Intranet Some organizations use Internet technologies to create their own privately accessible network called an intranet. If a connection to the Internet does exists, it does so through a firewall An intranet is almost always faster than the Internet

7. © 2002 by Prentice Hall 7 Firewall Firewall - a security gateway that protects an organization from unauthorized access via the Internet Consists of software and sometimes hardware components

8. © 2002 by Prentice Hall 8 Wireless Network Access Due to less reliability, inferior screen displays, and slower transfer rates, the traditional wired protocols are not appropriate for wireless environments. A few protocols have been developed which allow wireless devices to communicate via the Internet: –Wireless Application Protocol (WAP) –Wireless Markup Language (WML)

9. © 2002 by Prentice Hall 9 Multi-tier Architectures –Tiers are the number of computers (serving a like function) that a user must use to satisfy his/her request. –Common tiers include Web server and database server.

10. © 2002 by Prentice Hall 10 A Three-Tier Architecture

11. © 2002 by Prentice Hall 11 Functions of Tiers

12. © 2002 by Prentice Hall 12 Processing at the Different Tiers Since each tier serves a different function, each tier may have a different operating system and different application software offerings.

13. © 2002 by Prentice Hall 13 Processing Client Processing –Using the browser (e.g., Netscape Navigator) Server Processing –Using Server Software (e.g., ASP)

14. © 2002 by Prentice Hall 14 Windows 2000 Web Server Languages JavaScript VBScript Perl ActiveX Control Java

15. © 2002 by Prentice Hall 15 Standards & Languages Common With MS Web Server

16. © 2002 by Prentice Hall 16 Unix/Linux Web Server Environment JavaScript Java Applets Java Servlets Java Server Pages Perl Java CGI

17. © 2002 by Prentice Hall 17 N-Tier Processing The 3-Tier architecture may be extended to include additional tiers. This produces a distributed processing model using various servers on the Internet

18. © 2002 by Prentice Hall 18 Markup Languages Markup Languages are used to specify the appearance and behavior of Web Pages Markup Language flavors: –HTML – a subset of the SGML –DHTML –RDS/ADO –XML

19. © 2002 by Prentice Hall 19 HTML HyperText Markup Language –PROS Simple Standardized –CONS Static content Limited connectivity Mixed structure/content

20. © 2002 by Prentice Hall 20 DHTML Dynamic HyperText Markup Language Encapsulates the entire HTML command set Provides access to objects on the page using the Document Object Model (DOM) Allows for Cascading Style Sheets (CSS)

21. © 2002 by Prentice Hall 21 Data Services Data services allow Web pages to exchange data with databases RDS is a set of ObjectX controls –The data exchanges must be relatively simple ADO is a set of ActiveX Data Controls –These data exchanges may be more complex

22. © 2002 by Prentice Hall 22 Extensible Markup Language –XML XML clearly separates content from structure and allows developers to easily define their own elements. Rather than hard-coding Web pages, you create rules that govern how the document should look. Then merge the structure and the content files. So, the very nature of XML is dynamic.

23. © 2002 by Prentice Hall 23 Document Type Declaration – DTD A DTD defines the data content and may provide the data values While a DTD is desirable, it is not mandatory –XML documents using DTDs are termed type-valid documents –XML documents not using DTDs are termed not-type-valid documents

24. © 2002 by Prentice Hall 24 XML & CSS Similar to DHTML, Cascading Style Sheets (CSS) may be used with XML documents to present a consistent, standardized Web site.

25. © 2002 by Prentice Hall 25 Extensible Style Language Transformation –XMLT XMLT is used to transform one document into another document

26. © 2002 by Prentice Hall 26 XML Schema XML Schema is the next generation of DTD The schema itself is an XML document A W3 standard is currently being developed A document that conforms to an XML Schema is termed schema-valid.

27. © 2002 by Prentice Hall 27 XML Schema Concepts Simple Elements –Consist of a single content value Complex Elements –Consist of multiple content values

28. © 2002 by Prentice Hall 28 XML Namespaces Namespaces define where to look for files An XML document may have: –Up to one default namespace –Many labeled namespaces Naming conventions: –Must be unique within all schemas –Typically resembles a URL, but is not a URL

29. © 2002 by Prentice Hall 29 Wireless Application Protocol (WAP) WAP has been developed to facilitate Web development for wireless devices such as Personal Data Assistants (PDA) or cellular phones

30. © 2002 by Prentice Hall 30 WAP Server A WAP Server transforms XML documents into Wireless Markup Language (WML) – WML is a subset of XML A WML Scripting Language also exists

31. © 2002 by Prentice Hall 31 XML and Database Applications Any document that can process a DTD or XML Schema document can correctly interpret any arbitrary database view XML can easily process multiple multi-valued paths (several SQL statements would be required)

32. © 2002 by Prentice Hall 32 XML and Database Applications The separation of structure and content allows for: –The same data to be displayed in many different ways –The same structure (report) may be regenerated many times with different/updated data. –Permits document validation checking

33. © 2002 by Prentice Hall 33 OASIS –Document structures may be published and made publicly available –Organization for the Advancement of Structured Information Standards (OASIS): A clearinghouse for XML publications and schema standards

34. © 2002 by Prentice Hall 34 DBMS Integration of XML –Oracle XML DOM parser Xpath XSQL –SQL Server XML DOM parser Xpath ADO ASP

35. © 2002 by Prentice Hall 35 David M. Kroenke Database Processing Eighth Edition Chapter 14 Networks, Multi-Tier Architectures, and XML