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The first version of Jet was developed in , consisting of three modules which could be used to manipulate a database. Microsoft Access and Visual Basic use or have used Jet as their underlying database engine.
For larger database needs, Jet databases can be upgraded or, in Microsoft parlance, "up-sized" to Microsoft's flagship SQL Server database product. A five billion record MS Jet Red database with compression and encryption turned on requires about one terabyte of disk storage space [ citation needed ]. Jet, being part of a relational database management system RDBMS , allows the manipulation of relational databases.
It offers a single interface that other software can use to access Microsoft databases and provides support for security, referential integrity , transaction processing , indexing , record and page locking, and data replication.
In later versions, the engine has been extended to run SQL queries, store character data in Unicode format, create database views and allow bi-directional replication with Microsoft SQL Server.
Jet allows multiple users to access the database concurrently. To prevent that data from being corrupted or invalidated when multiple users try to edit the same record or page of the database, Jet employs a locking policy.
Any single user can modify only those database records that is, items in the database to which the user has applied a lock , which gives exclusive access to the record until the lock is released. In Jet versions before version 4, a page locking model is used, and in Jet 4, a record locking model is employed.
Microsoft databases are organized into data "pages", which are fixed-length 2 kB before Jet 4, 4 kB in Jet 4 data structures. Data is stored in "records" of variable length that may take up less or more than one page.
The page locking model works by locking the pages, instead of individual records, which though less resource-intensive also means that when a user locks one record, all other records on the same page are collaterally locked. As a result, no other user can access the collaterally locked records, even though no user is accessing them and there is no need for them to be locked.
In Jet 4, the record locking model eliminates collateral locks, so that every record that is not in use is available.
There are two mechanisms that Microsoft uses for locking : pessimistic locking , and optimistic locking. With pessimistic locking, the record or page is locked immediately when the lock is requested, while with optimistic locking, the locking is delayed until the edited record is saved. Conflicts are less likely to occur with optimistic locking, since the record is locked only for a short period of time.
However, with optimistic locking one cannot be certain that the update will succeed because another user could lock the record first. With pessimistic locking, the update is guaranteed to succeed once the lock is obtained. Other users must wait until the lock is released in order to make their changes. Lock conflicts, which either require the user to wait, or cause the request to fail usually after a timeout are more common with pessimistic locking.
Jet supports transaction processing for database systems that have this capability. A transaction is a series of operations performed on a database that must be done together — this is known as atomicity and is one of the ACID Atomicity, Consistency, Isolation, and Durability , concepts considered to be the key transaction processing features of a database management system. For transaction processing to work until Jet 3.
Until the transaction is committed, changes are made only in memory and not actually written to disk. One of the main advantages is that transactions can be abandoned if a problem occurs during the transaction. This is called rolling back the transaction, or just rollback, and it restores the state of the database records to precisely the state before the transaction began.
Transactions also permit the state of the database to remain consistent if a system failure occurs in the middle of a sequence of updates required to be atomic. There is no chance that only some of the updates will end up written to the database; either all will succeed, or the changes will be discarded when the database system restarts.
With ODBC's in-memory policy, transactions also allow for many updates to a record to occur entirely within memory, with only one expensive disk write at the end. Implicit transactions were supported in Jet 3. These are transactions that are started automatically after the last transaction was committed to the database.
However, it was found that this had a negative performance impact in bit Windows Windows 95, Windows 98 , so in Jet 3. Jet enforces entity integrity and referential integrity. Jet will by default prevent any change to a record that breaks referential integrity, but Jet databases can instead use propagation constraints cascading updates and cascading deletes to maintain referential integrity. Jet also supports "business rules" also known as "constraints" , or rules that apply to any column to enforce what data might be placed into the table or column.
Access to Jet databases is done on a per user-level. The user information is kept in a separate system database, and access is controlled on each object in the system for instance by table or by query.
Queries are the mechanisms that Jet uses to retrieve data from the database. The query is then compiled — this involves parsing the query involves syntax checking and determining the columns to query in the database table , then converted into an internal Jet query object format, which is then tokenized and organised into a tree like structure. In Jet 3. The query is then executed and the results passed back to the application or user who requested the data.
Jet passes the data retrieved for the query in a dynaset. This is a set of data that is dynamically linked back to the database. Instead of having the query result stored in a temporary table, where the data cannot be updated directly by the user, the dynaset allows the user to view and update the data contained in the dynaset.
Thus, if a university lecturer queries all students who received a distinction in their assignment and finds an error in that student's record, they would only need to update the data in the dynaset, which would automatically update the student's database record without the need for them to send a specific update query after storing the query results in a temporary table.
Jet originally started in as an underlying data access technology that came from a Microsoft internal database product development project, code named Cirrus. Cirrus was developed from a pre-release version of Visual Basic code and was used as the database engine of Microsoft Access. Tony Goodhew, who worked for Microsoft at the time, says. For VB [Visual Basic] 3. Jet became more componentised when Access 2.
A retrofit was provided that allowed Visual Basic 3. Jet 2. DLLs in Windows are "libraries" of common code that can be used by more than one application—by keeping code that more than one application uses under a common library which each of these applications can use independently code maintenance is reduced and the functionality of applications increases, with less development effort. The Jet DLL determined what sort of database it was accessing, and how to perform what was requested of it.
If the data source was an MDB file a Microsoft Access format then it would directly read and write the data to the file. If the data source was external, then it would call on the correct ODBC driver to perform its request. Jet 3. Jet 4. Microsoft Access versions from Access to Access included an "Upsizing Wizard" which could " upsize " upgrade a Jet database to "an equivalent database on SQL Server with the same table structure, data, and many other attributes of the original database".
Reports, queries, macros and security were not handled by this tool, meaning that some manual modifications might have been needed if the application was heavily reliant on these Jet features. It introduced a new default file format,. It also brought security changes and encryption improvements and enabled integration with Microsoft Windows SharePoint Services 3.
The engine in Microsoft Access discontinued support for Access 1. The driver is not part of the Windows operating system, but is available as a redistributable. The engine in Microsoft Access discontinued support for Access 95, Access 97 and xBase files, and it also discontinued support for replication. Version of Microsoft Access restored support for xBase files, [15] and Version introduced a Large Number data type.
From a data access technology standpoint, Jet is considered a deprecated technology by Microsoft, [17] but Microsoft continues to support ACE as part of Microsoft Access. Therefore, third party software support for JET databases is almost exclusively found on Windows. From Wikipedia, the free encyclopedia. Database engine built by Microsoft. This section does not cite any sources. Please help improve this section by adding citations to reliable sources.
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Upgrade to Microsoft Edge to take advantage of the latest features, security microsoft jet access 2016 free, and technical support. This utility may be run in conjunction with Microsoft Jet database engine 3. The reason for this is that midrosoft Microsoft Access Compact microsoft jet access 2016 free and the CompactDatabase method attempt to open and close a продолжить чтение before attempting /57164.txt compact it.
In certain cases where these utilities may not be able to reopen the database, Compact will be unable to proceed, preventing recovery of the database. Micorsoft additional information about how to download Microsoft Support files, click the following article number to view the article /29532.txt the Microsoft Knowledge Base:. Microsoft scanned this file for viruses. /41978.txt used the most current virus-detection software that was available on the date that the file was posted.
The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Table of contents Exit focus mode. Table of contents. In this article.
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