Unit – V Data Controls

A character is the most basic element of data that can be observed and manipulated. A field contains an item of data; that is, a character, or group of characters that are related. A record is composed of a group of related fields.

A database is a collection of information that is organized so that it can easily be accessed, managed, and updated. Database management systems are used to access and manipulate data in a database. A database management system is a software package that enables users to edit, link, and update files as needs dictate.

Data Controls: Visual Basic communicates with databases through the data control. Data controls can read, modify, delete, and add records to databases. The data control enables you to move around in a database from record to record and to display and manipulate data from the records in bound controls.

Data Access Objects (DAO): DAO (Data Access Objects) is an application program interface (API) available with Microsoft's Visual Basic that lets a programmer request access to a Microsoft Access database. DAO was Microsoft's first object-oriented interface with databases. DAO objects encapsulate Access's Jet functions. Through Jet functions, it can also access other Structured Query Language (SQL) databases.

Objects in DAO object model: The following are the various objects in DAO object model. Here is the object model’s hierarchy. Each object contains collections, methods and properties. A collection is a collection of objects of the same type. A method performs an operation on the object. A property contains a single attribute of the object.

Recordset: A DAO Recordset, represented in MFC (Microsoft Foundation Class) by a CDaoRecordset object. "A logical set of records. where Microsoft defines a record as "A set of related data about a person, place, event, or some other item. Table data is stored in records (rows) in the database. Each record is composed of a set of related fields (columns) - each field defining one attribute of information for the record.

DAO Recordset Types: You can create three kinds of Cdao Recordset objects: Table-type recordsets, representing a base table in a Microsoft Jet (.MDB) database Dynaset-type recordsets, which result from a query Snapshot-type recordsets, consisting of a static copy of a set of records The following table summarizes the characteristics and purposes of the three recordset types.

Data Report: A Data Report is similar to a VB form in that it has a visual designer and a code module. Using the visual designer, you can divide the report into two or more sections, each with its own headings.

Data Environment: Data Environment object is created and managed using Data Environment designer. A Data Environment object can accomplish any of the following tasks. • Can contain connection and command objects • Can establish relationship between command object to represent hierarchies • Can group data and get aggregates • Allows fields to be dragged and dropped on to a Data Report, for report, and a Form for data entry screen • Can work as source for Databound control such as DataCombo controls and Hierarchical Flexgrid control. .