April 20022/CS/3XAPP 1 Database Design Anatomy of an application John Wordsworth Department of Computer Science The University of Reading Room 129, Ext 6544

April 20022/CS/3XAPP 2 Lecture objectives To review the notion of an application To remind ourselves about the place of transactions in designing and application. To review interface design guidelines

April 20022/CS/3XAPP 3 What is an application? An application is a physical interface (group of screens) and database tables that provide a coherent set of transactions to support a particular business or administrative objective. An application may take the form of a single Delphi Project or a number of linked Projects. In MS Access an application may take the form of one or more.mdb files. In e-commerce, an application is a set of HTML pages, server programs, and databases.

April 20022/CS/3XAPP 4 An e-commerce application Database Web server Browser Tier 3Tier 2Tier 1

April 20022/CS/3XAPP 5 What is a transaction A single identifiable task with a definite objective, for which the user employs a software application A transaction may change the database in some way. A transaction may produce some (printed or displayed) output from the database.

April 20022/CS/3XAPP 6 Examples of transactions Student registration –Register a new student on a degree course –Register an existing student for one or more units –Print a list of students registered for a unit Bank account –Open an account –Enter a deposit transaction –Enter a direct debit mandate –Print a statement

April 20022/CS/3XAPP 7 Analysis of transactions What inputs are required? What outputs are expected? What changes to the relations in the database are expected? What errors should we guard against? What rate of usage should we expect? How important is this transaction to the users?

April 20022/CS/3XAPP 8 User interface design guidelines Use meaningful titles for screens and reports. Use familiar terminology in instructions. Keep related fields together – be consistent. Make the screen or report look attractive. Be consistent about the use of colours, terminology, abbreviations, and so on. Make the data entry areas clearly defined and of the right size, and show which fields are optional and which are required. Allow correction of errors for characters and entire fields. Produce sensible and informative error messages, free of value judgements. Provide help information for each field. Let the user know when the input is complete, and give an opportunity for review.

April 20022/CS/3XAPP 9 Permanent database files Hold the “strong entity types” plus the “weak entity types” created during logical database design Though records may be added and deleted, these files are not usually empty

April 20022/CS/3XAPP 10 Queries A group of operations (usually written in SQL) that perform routine transformations on tables In Access the term “query” includes select, update, delete, maketable, crosstab, etc. In Delphi these are handled by separate components (i.e. not grouped together under the general heading “queries”)

April 20022/CS/3XAPP 11 Reports Summarise information in the database Produce printed documents from database –invoices, catalogues, price-lists, monthly banking reports Facilities for subtotalling and grouping, headers and footers May be printed or displayed In Delphi see ReportSmith

April 20022/CS/3XAPP 12 Key points An application serves a group of users, and gives them an interface to transactions that access a database. Electronic commerce is a prominent source of database applications. User interface design needs care if the users are to be well-served.