Data Access

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General

The Data Access Layer is the tier of an application, where the actual sources are connected. In opposite to the Data Abstraction Layer, where the developer interacts with the data model on a higher level of abstraction, the data access usually encompasses not only information about the data sources but also about the means of connection like driver details.

Microsoft

Microsoft offers several types of data access components (Microsoft Data Access Components – MDAC), which compound of

All definitions—except for DAO— have been taken from Ozgrid (see link section).

Data Access Objects (DAO)

The Microsoft Jet Data Access Objects is a programming interface for database access in Microsoft Windows. It is considered to be deprecated for a long time but still in use. Due to reasons of backward compatibility the interface still exists. The benefit of DAO is the lightweight and straight forward use of the interface, which results in a relative flat learning curve.

The root node of the library is DBEngine, which provides access to Workspaces and Errors. A Workspace is a session in the database. The Workspace provides access to Databases, Groups and Users. A database object can be retrieved from Databases and gives the programmer access to Containers, QueryDefs, Recordsets, Relations and TableDefs and their respective properties.

ActiveX Data Objects (ADO)

ADO is the strategic application programming interface (API) to data and information. ADO provides consistent, high-performance access to data and supports a variety of development needs, including the creation of front-end database clients and middle-tier business objects that use applications, tools, languages, or Internet browsers. ADO is designed to be the one data interface needed for single and multi-tier client/server and Web-based data-driven solution development. The primary benefits of ADO are ease of use, high speed, low memory overhead, and a small disk footprint.

ADO provides an easy-to-use interface to OLE DB, which provides the underlying access to data. ADO is implemented minimal network traffic in key scenarios, and a minimal number of layers between the front end and data source-all to provide a lightweight, high-performance interface. ADO is easy to use because it uses a familiar metaphor-the COM automation interface, available from all leading Rapid Application Development (RAD) tools, database tools, and languages on the market today. ADO is a nice wrapper for OLD-DB.

Object Linking and Embedding Database (OLE DB)

OLE-DB is the Microsoft strategic system-level programming interface to data across the organization. OLE DB is an open specification designed to build on the success of ODBC by providing an open standard for accessing all kinds of data. Whereas ODBC was created to access relational databases, OLE DB is designed for relational and non relational information sources, including mainframe ISAM/VSAM and hierarchical databases; e-mail and file system stores; text, graphical, and geographical data; custom business objects; and more.

OLE DB defines a collection of COM interfaces that encapsulate various database management system services. These interfaces enable the creation of software components that implement such services. OLE DB components consist of data providers, which contain and expose data; data consumers, which use data; and service components, which process and transport data (such as query processors and cursor engines). OLE DB interfaces are designed to help components integrate smoothly so that OLE DB component vendors can bring high-quality OLE DB components to market quickly. In addition, OLE DB includes a bridge to ODBC to enable continued support for the broad range of ODBC relational database drivers available today.

Open Database Connectivity (ODBC)

The ODBC interface is an industry standard and a component of Microsoft Windows Open Services Architecture (WOSA). The ODBC interface makes it possible for applications to access data from a variety of database management systems (DBMSs). ODBC permits maximum interoperability-an application can access data in diverse DBMSs through a single interface. Furthermore, that application will be independent of any DBMS from which it accesses data. Users of the application can add software components called drivers, which create an interface between an application and a specific DBMS.

Use cases

When should you use OLE DB, ADO, DAO, or ODBC?

  • ADO is a wrapper around OLE DB so you can use ADO or OLE DB.
  • Non-OLE environment : If a database supports ODBC and and that database is on a server that does not support OLE then ODBC is the best choice.
  • Non-SQL environment : ODBC is designed to work with SQL. If you have non-SQL environment then OLE DB is the best choice.
  • OLE environment : If you already have ODBC drivers then you can use ODBC, otherwise use OLE-DB.
  • Interoperability required : If you need interoperable database components, then OLE DB is your best choice.
  • 16-Bit data access support : ADO does not support 16 bit so ODBC is the only choice.
  • Using multiple databases - If you are using databases that support Microsoft's jet engine then definite choice is ADO or DAO. By using ADO you get workspace level support for transaction. That means you can connect more than one database at a time in an application, which is impossible by using ODBC. You can only connect one database at a time by using ODBC.

ADO vs. DAO

ADO is a superset of DAO in functionality point of view. In fact ADO is a combination of DAO + RDO. I would prefer ADO in these cases. 1. If you are proficient in COM programming. 2. If your server supports OLE environment. 3. If you want workspace-level and multi database type ( Relational, indexed, ISAM type, text files supports ). DAO is best choice when you have DAO components installed on your machine and you are using Microsoft's jet database engine based databases such as MS-Access, SQL Server, MS-Excel or Paradox. This is fastest and easiest mathod o access databases.

DAO vs. ODBC

DAO is best choice when you have DAO components installed on your machine and you are using Microsoft's jet database engine based databases such as MS-Access, SQL Server, MS-Excel or Paradox. This is fastest and easiest method to access databases. ODBC is for various type of database which provides ODBC drives such as SQL Server, Oracle, MS-Access. Additional advantage is DAO is workspace-level support.

Advantages of DAO

Easy to use. Workspace level support. Both MFC and API provides DAO support. Speed is relatively faster than ODBC for jet database engine databases.

Advantages of ODBC

Easy to use specially when developer are not familiar with COM environment. SQL support. Both API and MFC support. Good for relational databases only.

Advantages of ADO or OLE-DB

Workspace-level support. Fastest method to access various kind of databases. Easy to use fi you are familiar with COM environment. Provides access to relational, non relational and other types of data.

Links

ozgrid connectionstrings

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