1. 1 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Survey on Database Architectures A. Bacioccola

2. 2 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Outlines Desktop Database Application Client / Server Architecture Client / Server Database PostgreSQL

3. 3 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Desktop Database Application (1) A desktop database is used by small businesses, and hobby programmers to create ad-hoc customized desktop systems for handling the creation and manipulation of data; An example of desktop dabatase is Office Access, previously known as Microsoft Access. Access allows relatively quick development because all database tables, queries, forms, and reports are stored in the database. For query development, Access utilizes the Query Design Grid, a graphical user interface that allows users to create queries without knowledge of the SQL programming language.

4. 4 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Desktop Database Application (2) In the Query Design Grid, users can "show" the source tables of the query and select the fields they want returned by clicking and dragging them into the grid. Joins can be created by clicking and dragging fields in tables to fields in other tables. Access allows users to view and manipulate the SQL code if desired. Access can be applied to small projects which involve more than one user. In this scenario, it scales poorly to larger projects involving multiple concurrent users because it is a desktop application, not a true client-server database. When a Microsoft Access database is shared by multiple concurrent users, processing speed suffers. The effect is dramatic when there are more than a few users or if the processing demands of any of the users are high.

5. 5 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Client / Server Architecture (1) Client server is network architecture which separates a client (often an application that uses a graphical user interface) from a server. Each instance of the client software can send requests to a server. Specific types of servers include web servers, application servers, file servers, terminal servers, and mail servers. While their purposes vary somewhat, the basic architecture remains the same.

6. 6 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Client / Server Architecture (2) Although this idea is applied in a variety of ways, on many different kinds of applications, the easiest example to visualize is the current use of web pages on the internet. For example, if you are reading an article on Wikipedia, your computer and web browser would be considered a client, and the computers, databases, and applications that make up Wikipedia would be considered the server. When your web browser requests a particular article from Wikipedia, the Wikipedia server finds all of the information required to display the article in the Wikipedia database, assembles it into a web page, and sends it back to your web browser for you to look at.

7. 7 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Client / Server Database (1) Advantages of Client/Server database over desktop Database: Scalability: the client/server database architecture allows more than one user to concurrently access the database; all the accesses to the database are efficiently managed by the server; Security: Access control techniques can be implemented. Only authorized users can write the database; Robustness : database server applications typically implement strategies against hardware failures and data loss. Portability: the client applications does not have to implement the whole database structure, but only methods to retrieve data.

8. 8 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Client / Server Database (2) Disadvantages of Client/Server database over desktop Database: Complexity: the client/server database requires more effort to be implemented and managed compared to the desktop Database;

9. 9 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola PostgreSQL PostgreSQL is a free software object-relational database management system (ORDBMS), released under a BSD-style license. It offers an alternative to other database systems. Similarly to other free software projects such as Apache, GNU/Linux, and MediaWiki, PostgreSQL is not controlled by any single company, but relies on a global community of developers and companies to develop it.

10. 10 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola Data Types Comparison The "same, yet different" nature of SQL data types is of vital importance for any developer working with multiple database products, or those valiantly attempting to write SQL that lives in the application layer, independent of specific database platform choices. While by no means complete, the following table outlines some of the common names of data types between the various database platforms: AccessSQL-ServerMySQLPostgreS QL booleanYes/NoBitN/ABoolean integerNumber (integer) IntInt Integer (synonyms) Integer Int floatNumber (single) Float Real FloatNumeric currencyCurrencyMoneyN/AMoney string (fixed) N/AChar string (variable) Text (<256) Memo (65k+) Varchar Ask your question s for John Paul here! Post your commen ts Post your commen ts Also in aboutS QL: Working With Tables Data Definitio n Languag e Introduci ng SQL Sets As you can see, similarities aboun

11. 11 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola References Wikipedia: http://en.wikipedia.org/ Index terms: Database Client-server Postgresql Microsoft Access PostgreSql: http://www.postgresql.org/

12. 12 ©2007, University of Pisa, Dip. Ingegneria dell’Informazione – Andrea Bacioccola DISCUSSION