Class or table locking means that all instances of either a class or table are locked, as is illustrated below. This shows one form of concurrency control. Note the circle at the lower left. It represents all instances of a class, regardless of the page where they are stored.

Cluster locking or container locking for concurrency control is illustrated in the figure below. In this form of locking, all data clustered together (on a page or multiple pages) will be locked simultaneously. This applies only to clusters of objects in ODBMSs. Note that in this example, the cluster of objects spans portions of three pages.

Page locking (or page-level locking) concurrency control is shown in the figure below. In this situation, all the data on a specific page are locked. A page is a common unit of storage in computer systems and is used by all types of DBMSs. In this figure, each rectangle represents a page. Locking for objects is on the left and page locking for relational tuples is on the right. If the concept of pages is new to you, just think of a page as a unit of space on the disk where multiple data instances are stored.

Concurrency control and locking is the mechanism used by DBMSs for the sharing of data. Atomicity, consistency, and isolation are achieved through concurrency control and locking.

Maintaining updates of committed transactions is critical. These updates must never be lost. The ACID property of durability addresses this need. Durability refers to the ability of the system to recover committed transaction updates if either the system or the storage media fails. Features to consider for durability:

The isolation portion of the ACID properties is needed when there are concurrent transactions. Concurrent transactions are transactions that occur at the same time, such as shared multiple users accessing shared objects. This situation is illustrated at the top of the figure as activities occurring over time. The safeguards used by a DBMS to prevent conflicts between concurrent transactions are a concept referred to as isolation.

Consistency is the ACID property that ensures that any changes to values in an instance are consistent with changes to other values in the same instance. A consistency constraint is a predicate on data which server as a precondition, post-condition, and transformation condition on any transaction.

The phrase "all or nothing" succinctly describes the first ACID property of atomicity. When an update occurs to a database, either all or none of the update becomes available to anyone beyond the user or application performing the update. This update to the database is called a transaction and it either commits or aborts. This means that only a fragment of the update cannot be placed into the database, should a problem occur with either the hardware or the software involved. Features to consider for atomicity:

ACID properties are an important concept for databases. The acronym stands for Atomicity, Consistency, Isolation, and Durability.

Object DBMSs allow you to store objects directly without any mapping to different data structures. Relational DBMSs require mapping from objects to tables. This mapping to different data structures is called "impedance mismatch." The figure below shows direct storage at the left and impedance mismatch at the right.

Transparent persistence in object database products refers to the ability to directly manipulate data stored in a database using an object programming language. This is in contrast to a database sub-language used by embedded SQL or a call interface used by ODBC or JDBC. Using an object database product means that you have higher performance and less code to write.

DataObjects.NET is an object persistence layer for the .NET Framework. It dramatically decreases development time by handling all persistence-related tasks transparently. It completely supports inheritance (including interfaces), relations and collections, transactions, object queries, full-text indexing and search, multilingual properties and a lot of other features. Moreover, it provides a set of unique services including automatic transaction management and built-in access control system. Its feature set allows building not only the data access tier with it, but the complete business tier of a complex application.

Memory Database puts all data into the memory. Since most database transactions can be done in the memory without disk access, it can perform 10 to 100 times faster than the traditional database system. It is the best solution for the companies who have a lot of data, computations and concurrent users.

DBF Viewer 2000 is the powerful, compact and easy-to-use viewer and editor for DBF files (Clipper, dBase, FoxBase, Foxpro, Visual Foxpro, Visual DBase, VO, DB2K...).

EasyStruct is the proven database structure documentation and migration tool. It documents the complete structure of a database and generates output as XML, HTML or Microsoft Word documents.

dbQwikEdit is your data central. For beginners to pros, getting to your data has never been easier. Powerful, yet simple. Take control of your data today.

ATAF can automatic convert the database design and copy the data from a MS-Access database and create it on a mySQL server in one of the 4 following ways.

Access2MySQL Pro is an efficient converter which performs MS Access (mdb) to MySQL and MySQL to Access database conversions simply by configuring several options in wizard-like application. Whether you want to copy a whole database or convert a number of tables, our program is at your service. Our user-friendly and cost-effective product offers you maximum simplicity and convenience, they are easy to use and really simple to maintain and upgrade.

Data Quik - The Database File Copier allows you to copy selected fields and records between some of the major Database Files. In general terms, Data Quik-The Database Copy Utility is an add on Database utility that performs the following functions:

VolgaDB Engine is a small and fast single-user engine for working with flat files in own Volga format or client-server multi-user engine for working with MSSQL, MySQL, MS Access, dBASE databases without using BDE.