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Microsoft access Microsoft access Document Transcript

  • Microsoft AccessMicrosoft Office Access, previously known as Microsoft Access, is adatabasemanagement system from Microsoft that combines the relationalMicrosoft Jet DatabaseEngine with a graphical user interface and software-development tools. It is a member ofthe Microsoft Office suite of applications, included in the Professional and higher editions orsold separately. On May 12, 2010, the current version of Microsoft Access 2010 wasreleased by Microsoft in Office 2010; Microsoft Office Access 2007 was the prior version.MS Access stores data in its own format based on the Access Jet Database Engine. It canalso import or link directly to data stored in other applications and databases.[1]Software developers and data architects can use Microsoft Access to developapplicationsoftware, and "power users" can use it to build software applications. Like other Officeapplications, Access is supported by Visual Basic for Applications, an object-oriented programming language that can reference a variety of objects including DAO (DataAccess Objects), ActiveXData Objects, and many other ActiveX components. Visual objectsused in forms and reports expose their methods and properties in the VBA programmingenvironment, and VBA code modules may declare and call Windows operating-system functions.UsesIn addition to using its own database storage file, Microsoft Access may also be used as thefront-end with other products as the back-end tables, such as Microsoft SQL Server andnon-Microsoft products such as Oracle and Sybase. Multiple backend sources can be usedby a Microsoft Access Jet Database (accdb and mdb formats). Similarly, some applicationswill only use the Microsoft Access tables and use another product as a front-end, suchas Visual Basic or ASP.NET. Microsoft Access may be only part of the solution in morecomplex applications, where it may be integrated with other technologies such as MicrosoftExcel, Microsoft Outlookor ActiveX Data Objects.Access tables support a variety of standard field types, indices, and referential integrity.Access also includes a query interface, forms to display and enter data, and reports forprinting. The underlying Jet database, which contains these objects, is multiuser-aware andhandles record-locking and referential integrity including cascading updates and deletes.Repetitive tasks can be automated through macros with point-and-click options. It is alsoeasy to place a database on a network and have multiple users share and update datawithout overwriting each others work. Data is locked at the record level which is significantlydifferent from Excel which locks the entire spreadsheet.There are template databases within the program and for download from their website.These options are available upon starting Access and allow users to enhance a database
  • with predefined tables, queries, forms, reports, and macros. Templates do not includeVBA code.Programmers can create solutions using the programming language Visual Basic forApplications (VBA), which is similar to Visual Basic 6.0 (VB6) and used throughoutthe Microsoft Office programs such as Excel, Word, Outlook and PowerPoint. Most VB6code, including the use of Windows API calls, can be used in VBA. Power users anddevelopers can extend basic end-user solutions to a professional solution with advancedautomation, data validation, error trapping, and multi-user support.The number of simultaneous users that can be supported depends on the amount of data,the tasks being performed, level of use, and application design. Generally accepted limitsare solutions with 1 GB or less of data (Access supports up to 2 GB) and performs quite wellwith 100 or fewer simultaneous connections (255 concurrent users are supported). Thiscapability is often a good fit for department solutions. If using an Access database solution ina multi-user scenario, the application should be "split". This means that the tables are in onefile called the back end (typically stored on a shared network folder) and the applicationcomponents (forms, reports, queries, code, macros, linked tables) are in another file calledthe front end. The linked tables in the front end point to the back end file. Each user of theAccess application would then receive his or her own copy of the front end file.Applications that run complex queries or analysis across large datasets would naturallyrequire greater bandwidth and memory. Microsoft Access is designed to scale to supportmore data and users by linking to multiple Access databases or using a back-end databaselike Microsoft SQL Server. With the latter design, the amount of data and users can scaleto enterprise-level solutions.Microsoft Accesss role in web development prior to version 2010 is limited. Userinterface features of Access, such as forms and reports, only work in Windows. In versions2000 through 2003 an Access object type called Data Access Pages created publishableweb pages. Data Access Pages are no longer supported. The Microsoft Jet DatabaseEngine, core to Access, can be accessed through technologies such as ODBC or OLE DB.The data (i.e., tables and queries) can be accessed by web-based applications developedin ASP.NET, PHP, or Java.Access 2010 allows databases to be published to SharePoint 2010 web sitesrunning Access Services. These web-based forms and reports run in any modern webbrowser. The resulting web forms and reports, when accessed via a web browser, dontrequire any add-ins or extensions (e.g. ActiveX, Silverlight).A compiled version of an Access database (File extensions: .MDE /ACCDE or .ADE;ACCDE only works with Access 2007 or later) can be created to prevent user fromaccessing the design surfaces to modify module code, forms, and reports. An MDE/ACCDEfile is a Microsoft Access database file with all modules compiled and all editable sourcecode removed. An ADE file is an Access project file with all modules compiled and alleditable source code removed. Both the .MDE/ACCDE and .ADE versions of an Accessdatabase are used when end-user modifications are not allowed or when the application’ssource code should be kept confidential.Microsoft offers a runtime version of Microsoft Access 2007 for download. This allows peopleto create Access solutions and distribute it for use by non-Microsoft Access owners (similarto the way DLLs or EXEs are distributed). Unlike the regular version of Access, the runtimeversion allows users to use the Access application but they cannot use its design surfaces.
  • Microsoft also offers developer extensions for download to help distribute Accessapplications, create database templates, and integrate source code control with MicrosoftVisual SourceSafe.FeaturesUsers can create tables, queries, forms and reports, and connect them togetherwith macros. Advanced users can use VBA to write rich solutions with advanced datamanipulation and user control. Access also has report creation features that can work withany data source that Access can "access".The original concept of Access was for end users to be able to "access" data from anysource. Other features include: the import and export of data to many formatsincluding Excel, Outlook, ASCII, dBase, Paradox, FoxPro, SQL Server, Oracle, ODBC, etc. Italso has the ability to link to data in its existing location and use it for viewing, querying,editing, and reporting. This allows the existing data to change while ensuring that Accessuses the latest data. It can perform heterogeneous joins between data sets stored acrossdifferent platforms. Access is often used by people downloading data from enterprise leveldatabases for manipulation, analysis, and reporting locally.There is also the Jet Database format (MDB or ACCDB in Access 2007) which can containthe application and data in one file. This makes it very convenient to distribute the entireapplication to another user, who can run it in disconnected environments.One of the benefits of Access from a programmers perspective is its relative compatibilitywith SQL (structured query language) — queries can be viewed graphically or edited as SQLstatements, and SQL statements can be used directly in Macros and VBA Modulestomanipulate Access tables. Users can mix and use both VBA and "Macros" for programmingforms and logic and offers object-oriented possibilities. VBA can also be included in queries.Microsoft Access offers parameterized queries. These queries and Access tables can bereferenced from other programs like VB6 and.NET through DAO or ADO. From MicrosoftAccess, VBA can reference parameterized stored procedures via ADO.The desktop editions of Microsoft SQL Server can be used with Access as an alternative tothe Jet Database Engine. This support started with MSDE (Microsoft SQL Server DesktopEngine), a scaled down version of Microsoft SQL Server 2000, and continues with the SQLServer Express versions of SQL Server 2005 and 2008.Microsoft Access is a file server-based database. Unlike client–server relational databasemanagement systems (RDBMS), Microsoft Access does not implement databasetriggers, stored procedures, or transaction logging. Access 2010 includes table-level triggersand stored procedures built into the ACE data engine. Thus a Client-server database systemis not a requirement for using stored procedures or table triggers with Access 2010. Tables,queries, Forms, reports and Macros can now be developed specifically for web baseapplication in Access 2010. Integration with Microsoft SharePoint 2010 is also highlyimproved.
  • Access Services and Web databaseASP.NET web forms can query an MS Access database, retrieve records and display themon the browserSharePoint Server 2010 via Access Services allows for Access 2010 databases to bepublished to SharePoint, thus enabling multiple users to interact with the databaseapplication from any standards-compliant Web browser. Access Web databases publishedto SharePoint Server can use standard objects such as tables, queries, forms, macros, andreports. Access Services stores those objects in SharePointDevelopmentAccess stores all database tables, queries, forms, reports, macros, and modules in theAccess Jet database as a single file.For query development, Access offers a "Query Designer", a graphical user interface thatallows users to build queries without knowledge of the SQL programming language. In theQuery Designer, users can "show" the data sources of the query (which can be tables orqueries) and select the fields they want returned by clicking and dragging them into the grid.One can set up joins by clicking and dragging fields in tables to fields in other tables. Accessallows users to view and manipulate the SQL code if desired. Any Access table, includinglinked tables from different data sources, can be used in a query.Access also supports the creation of "pass-through queries". These snippets of SQL codecan address external data sources through the use of ODBC connections on the localmachine. This enables users to interact with data stored outside the Access program withoutusing linked tables or Jet Users construct the pass-through queries using the SQL syntaxsupported by the external data source.When developing reports that are linked to queries placing or moving items in the designview of the report, Access runs the linked query in the background on any placement ormovement of an item in that Report. If the report is linked to a query that takes a long time toreturn records this means having to wait until the query has run before you can add/edit ormove the next item in the report (this feature cannot be turned off).Non-programmers can use the macro feature to automate simple tasks through a series ofdrop-down selections. Macros allow users to easily chain commands together such asrunning queries, importing or exporting data, opening and closing forms, previewing andprinting reports, etc. Macros support basic logic (IF-conditions) and the ability to call othermacros. Macros can also contain sub-macros which are similar to subroutines. In Access2007 enhanced macros with the inclusion of error-handling and of support for temporaryvariables. Access 2007 also introduced embedded macros that are essentially properties ofan objects event. This eliminated the need to store macros as individual objects. Macroshowever, are limited in their functionality by a lack of programming loops and of advancedcoding logic. Most professional Access developers use the VBA programming language for aricher and more powerful development environment.The programming language available in Access is, as in other products of the MicrosoftOffice suite, Microsoft Visual Basic for Applications, which is nearly identical to Visual Basic6.0 (VB6). VBA code can be stored in modules and code behind forms and reports. Modulescan also be classes.
  • To manipulate data in tables and queries in VBA, Microsoft provides two database accesslibraries of COM components:1. Data Access Objects (DAO) (32-bit only), which is included in Access and Windowsand evolved to ACE in Microsoft Access 2007 for the ACCDE database format2. ActiveX Data Objects ActiveX Data Objects (ADO) (both 32-bit and 64-bit versions)Beside DAO and ADO, developers can also use OLE DB and ODBC for developing nativeC/C++ programs for Access.[24]For ADPs and the direct manipulation of SQL Server data,ADO is required. DAO is most appropriate for managing data in Access/Jet databases, andthe only way to manipulate the complex field types in ACCDB tables.In the database container or navigation pane of Access 2007, the system automaticallycategorizes each object by type. Many Access developers use the Leszynski namingconvention, though this is not universal; it is a programming convention, not a DBMS-enforced rule.[25]It is particularly helpful in VBA where references to object names may notindicate its data type (e.g. tbl for tables, qry for queries).Developers deploy Microsoft Access most often for individual and workgroup projects (theAccess 97 speed characterization was done for 32 users).[26]Since Access 97, and withAccess 2003 and 2007, Microsoft Access and hardware have evolved significantly.Databases under 1 GB in size (which can now fit entirely in RAM) and 50 simultaneoususers are well within the capabilities of Microsoft Access. Of course, performance dependson the database design and tasks. Disk-intensive work such as complex searching andquerying take the most time.As data from a Microsoft Access database can be cached in RAM, processing speed maysubstantially improve when there is only a single user or if the data are not changing. In thepast, the effect of packet latency on the record-locking system caused Access databases torun slowly on a Virtual Private Network (VPN) or a Wide Area Network (WAN) against a Jetdatabase. As of 2010broadband connections have mitigated this issue. Performance canalso be enhanced if a continuous connection is maintained to the back-end databasethroughout the session rather than opening and closing it for each table access. If AccessDatabase performance over VPN or WAN suffers, then a client using Remote DesktopProtocol (such as Microsoft Terminal Services) can provide an effective solution. Accessdatabases linked to SQL Server or to Access Data Projects work well over VPNs and WANs.In July 2011, Microsoft acknowledged an intermittent query performance problem with allversions of Access and Windows 7 and Windows Server 2008 R2 due to the nature ofresource management being vastly different in newer operating systems.[27]This issueaffects query performance severely on both Access 2003 and earlier with the Jet DatabaseEngine code as well as Access 2007 and later with the Access Database Engine(ACE).[27]Microsoft has issued hot fixes KB2553029 for Access 2007 and KB2553116 forAccess 2010, but will not fix the issue with Jet 4.0 as it is out of mainstream supportProtectionMicrosoft Access offers several ways to secure the application while allowing users toremain productive.The most basic is a database password. Once entered, the user has full control of all thedatabase objects. This is a relatively weak form of protection which can be easily cracked.
  • A higher level of protection is the use of workgroup security requiring a user name andpassword. Users and groups can be specified along with their rights at the object type orindividual object level. This can be used to specify people with read-only or data entry rightsbut may be challenging to specify. A separate workgroup security file contains the settingswhich can be used to manage multiple databases. Workgroup security is not supported inthe Access 2007 and Access 2010 ACCDB database format, although Access 2007 andAccess 2010 still support it for MDB databases.Databases can also be encrypted. The ACCDB format offers significantly advancedencryption from previous versionsAdditionally, if the database design needs to be secured to prevent changes, Accessdatabases can be locked/protected (and the source code compiled) by converting thedatabase to a .MDE file. All changes to the VBA project (modules, forms, or reports) need tobe made to the original MDB and then reconverted to MDE. In Access 2007 and Access2010, the ACCDB database is converted to an ACCDE file. Some tools are available forunlocking and "decompiling", although certain elements including original VBA commentsand formatting are normally irretrievable.File extensionsMicrosoft Access saves information under the following file formats:File format ExtensionProtected Access Project .adeAccess Project .adpAccess Blank Project Template .adnAccess Database (2007) .accdbAccess Database Runtime (2007) .accdrAccess Database Template (2007) .accdtAccess Database (2003 and earlier) .mdb
  • Access Database, used for addins (2,95,97), previously used for workgroups (2). .mdaAccess Blank Database Template (2003 and earlier) .mdnAccess Add-in Data (2003 and earlier) .mdtAccess Workgroup, database for user-level security. .mdwAccess (SQL Server) detached database (2000) .mdfProtected Access Database, with compiled VBA (2003 and earlier) .mdeProtected Access Database, with compiled VBA (2007) .accdeWindows Shortcut: Access Macro .mamWindows Shortcut: Access Query .maqWindows Shortcut: Access Report .marWindows Shortcut: Access Table .matWindows Shortcut: Access Form .maf