Notes de cours Access.docx

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Concordia University
Business Technology Management
BTM 481

Navigating Among the Objects in an Access DatabaseThe objects in an Access database are the main components that are created and used to make the database function The four main object types are tables queries forms and reports Two other object types macros and modules are used less frequentlyA field is the smallest data element contained in a table Fields define the type of data that is collected for example text numeric or date A field may be required or optionalA record is a complete set of all of the data elements fields about one person place event or conceptA table the foundation of every database is a collection of related recordsA database consists of one or more tables to store data one or more forms to enter data into the tables and one or more reports to output the table data as organized informationThe main functions of a database are to collect data to store data logically to manipulate data to make it more useful and to output the data to the screen and printed reportsDatabases also export data to files so the files can be imported by other databases or other informationprocessing systemsExamine the Access InterfaceThe Navigation Pane organizes and lists the database objects in an Access databaseAs stated earlier six types of objectstables queries forms reports macros and modules can exist in a databaseMost databases contain multiple tables queries forms and reports Tables store the data forms enable users to enter information into the tables reports enable users to display data in an organized format and queries enable users to ask questions about the dataThe Access Ribbon contains the icons that help you perform the database functions to maintain a databaseWork with Table ViewsThe Datasheet view is a grid containing columns fields and rows records similar to an Excel spreadsheet You can view add edit and delete records in the Datasheet viewDesign view is used to create and modify a tables design by specifying the fields it will contain the fields data types and their associated properties Data types define the type of data that will be stored in a field such as currency numeric text etcThe primary key is the field or combination of fields that uniquely identifies each record in a tableNo system no matter how sophisticated can produce valid output from invalid input Access database systems are built to anticipate data entry errors These systems contain table validation rules created to prevent invalid data entry Two types of validation rules existthose built into Access and those a developer createsspecifically for a database ExAccess will automatically prevent you from adding a new record with the same primary key as an existing record Access does not allow you to enter text or numeric data into a date fieldUse Forms Queries and ReportsThe tables are the heart of any database because they contain the actual data The other objects in a databasesuch as forms queries and reportsare based on one or more underlying tablesA form is an object that enables you to enter modify or delete table data A form enables you to manipulate data in the same manner that you would in a tables Datasheet view The difference is that you can create a form that will limit the user to viewing only one record at a timeA query is a question that you ask about the data in the tables of your database The answer is shown in the query results A query can be used to display only records that meet a certain criterion and only the fields that are requiredA criterion criteria pl is a number a text phrase or an expression used to filter the records in a table If you need the names of all the suppliers in Quebec you can set the suppliers stateprovince criterion to Quebec The results would yield only those suppliers from Quebec Query results are in Datasheet view and are similar in appearance to the underlying table except that the query contains selected records andor selected fields for those records The query also may list the records in a different sequence from that of the tableA report contains professionallooking formatted information from underlying tables or queriesUnderstanding the Difference Between Working in Storage and in MemoryWord Excel and PowerPoint all work primarily from memory In those applications your work is not automatically saved to your hard drive unless you click the save icon Access on the other hand works primarily from storage With an Access database file several users can work in the same file at the same timePractising Good Database File ManagementAccess runs best from a local disk drive or network disk drive because those drives have sufficient access speed to support the software Access speed measures the time it takes for the storage device to make the file content available for use Your next best storage option is a thumb drive also known as a USB jump drive a flash drive a pen drive or a stick driveBacking Up Compacting and Repairing Access FilesAccess provides two utilities to help protect the data within a database Compact and Repair and Backup These two functions both help protect your data but they each serve a different purpose Compact and Repair reduces the size of the database Backup creates a duplicate copy of the databaseCompact and Repair a DatabaseAll Access databases have a tendency to expand with everyday use Entering data creating queries running reports deleting objects and adding indexes will all cause a database file to expand This growth may increase storage requirements and may also impact database performanceWhen you run the Compact and Repair utility it creates a new database file behind the scenes and copies all the objects from the original database into the new one As it copies the objects into the new file Access will remove temporary objects and unclaimed space due to deleted objects resulting in a smaller database file Compact and Repair will also defragment a fragmented database file if neededBack Up a Database
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