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BSc. CS Module Instructor: Mr. Abubakar, H Lecture No. 3 : Database Connectivity - DAO and ADO 2009/2010 Visual Programming – CIT 737
BSc. CS
Module Instructor: Mr. Abubakar, H
Lecture No. 3 : Database Connectivity - DAO and ADO
2009/2010
Visual Programming – CIT 737
File System Critique
File System Data Management
Requires extensive programming in third-generation
language (3GL)
Time consuming
Makes ad hoc queries impossible: user-defined queries
Leads to islands of information
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File System Critique (con’t.)
Data Dependence
Change in file’s data characteristics requires modification of
data access programs
Must tell program what to do and how
Makes file systems cumbersome from programming and data
management views
Structural Dependence
Change in file structure requires modification of related
programs
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File System Critique (con’t.)
Field Definitions and Naming Conventions
Selection of proper field names important
Attention to length of field names
Use of unique record identifiers
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File System Critique (con’t.)
Data Redundancy
Different and conflicting versions of same data
Results of uncontrolled data redundancy
Data anomalies
- Modification
- Insertion
- Deletion
Data inconsistency
- Lack of data integrity
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Database Systems
Database consists of logically related data stored in a single
repository
Provides advantages over file system management approach
Eliminates inconsistency, data anomalies, data dependency, and
structural dependency problems
Stores data structures, relationships
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Database vs. File Systems
Figure 1.6
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Database System Environment
Figure 1.7
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DBMS Functions
Data dictionary management
Data storage management
Data transformation and presentation
Security management
Multiuser access control
Backup and recovery management
Data integrity management
Database language and application
programming interfaces
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What is DAO????
DAO is an object oriented interface to Microsoft Jet database
engine which enables you to;
- access
- manipulate data programmatically in local and remote databases
DAO communicates with MS office DBs and other ODBC
compliant data sources through the Jet Engine
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What DAO do
Data Access Objects (DAO) provides methods for:
- creating databases
- defining tables, fields, and indexes
- establishing relations between tables
- navigating and querying the database, and so on
DAO model is a collection of object classes that provide
properties and methods for database programming
DAO connects to both MS Access and ODBC
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Overview of DAO and Jet
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Jet Database Engine
The Jet database engine does the followings:
- allows manipulation of a Relational Database (Query Manager)
- offers a single interface that S/W use to access DBs (Jet API)
- supports security, RI, Transaction Processing, indexing, and so on
- is the part of RDBMS
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Jet Database Engine…
This approach has the following advantages
- Simplifies access to the DB
- Insulates the DB from the underlying mechanics of
retrieving and updating data
- Affords great flexibility because the same objects,
properties and methods can be used with a wide variety of
supported DB formats
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ODBC Driver Manager
ODBC driver manager
- is the software layer between jet Engine and ODBC drivers
- responsible for loading and unloading of appropriate drivers
- portability, Runtime binding to DS, and so on.
ODBC Driver: is a software interface that
- accepts ODBC standard queries
- passes them through to the specific application (DB Servers)
- modifying where necessary to account for application specific
database structure and format
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Remote and ISAM manager
Remote Manager is a software solution that will allow you to
manage all your remote control connections in a single place
ISAM Manager is a software solution that will allow you to
manage all your Indexed Sequential Access Method databases
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VB 6.0 Supported DBs
Through DAO and the JET engine, VB6 recognizes three
categories of DBs:
VB 6.0 DBs: Such as MS Access, are called native databases
- fast and easy
External DBs: these are Indexed Sequential Access Method
(ISAM) databases in several formats. E.g. dBase III, dBase IV, and
so on.
ODBC DBs: these include client/server databases that conform
to the ODBC standard, such as Microsoft SQL Server and Oracle.
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Why DAO???
The DAO programming model provides:
- advanced resultset management
- universal programming model that can access any ODBC database
regardless of the ODBC compliance level
- universal error management
When to use DAO
- Is the only data access technology that supports 16-bit operations
- If an application must access both native Microsoft Jet and ODBC
resources, DAO is the best choice.
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Data Access Objects (DAO)…
DAO library
Visual Basic 6.0 includes DAO version 3.51. To access these
objects, a reference must be made to the DAO object library.
- Project References
This will display the References dialog box
Select Microsoft DAO 3.6 object library and click OK
- DAO 3.51 is the "proper" library for use with Access 97
- DAO 3.6 is the one for Access 2000 and newer
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The DAO Model
The DAO Model
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Data Access Objects
DBEngine object: holds all other objects
- CreateWorkspace()
Workspace object: defines a session for the user, an area can hold one
or more databases
- CreateDatabase()
- OpenDatabase()
- BeginTrans()
- CommitTrans(), Rollback()
TableDef Object : describes database tables
- createIndex()
- createField()
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Data Access Objects…
QueryDef: represents a stored SQL query statement, with zero
or more parameters, maintained in a Microsoft Jet database
- Execute()
- OpenRecordSet()
RecordSet: carries data to and from the DB
- AddNew()
- Edit()
- Update
- CancelUpdate
- Delete
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Data Access Objects…Navigation Methods
- MoveFirst()
- MoveNext()
- MovePrevious()
- MoveLast()
- Move()
Search Methods
- FindFirst()
- FindNext()
- FindPrevious()
- FindLast()
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Data Access Objects…
Relation object: represents a relationship between fields in
tables and queries
- CreateField()
Field object: represents a field in a table, query, relation, or
recordset
1. contains data
2. reads data from a record
3. writes data into a record
Index object: represents an index on a table in the database
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Data Access Objects…
Parameter object: represents a value associated with a
QueryDef object
- Query parameters can be input, output, or both
Error object: contains information about an error that occurred
during a DAO operation
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ActiveX Data Objects (ADO)
ActiveX Data Objects (ADO)
- is an Object Oriented database access technology.
- is a part of Microsoft’s Universal Data Access initiative, which
seeks to make all data sources generic
ADO uses OLEDB as its middleware
Why ADO
- ADO can be used in Visual Basic with no problem
- Easier to connect than DAO and RDO
- ADO’s performance today is much better than DAO and RDO
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ActiveX Data Objects (ADO)…
OLE DB has three types of components
- Data providers
- Data Consumers
- Service components
Data providers:
- are application containing data that other appls need
- expose OLE DB interfaces that service components or data
consumers can access directly.eg MS SQL Server, OS component
There is also OLE DB provider for ODBC
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ActiveX Data Objects (ADO)…
Data Consumers
- are applications that use data exposed by the DPs
- ADO is a programmatic interface for using OLE DB
- any program using ADO is an OLE DB consumer
Service Components are components of OLE DB that
- process
- transport data
these components include query processor and cursor engines
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Why ADO???
Primary benefits of ADO
- Easy of use: b’se of flat objects model
- High speed/performance: indexed fields
- Low memory overhead : indexes and less no. of objects
- small disk footprint: less number of objects
- ADO is intended to give you a consistent interface for working
with a wide variety of data sources;
text files
ODBC relational databases
complex groups of databases
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ADO characteristics
Characteristics of ADO
- Flat objects model: no need of hierarchical creation
- Less number of objects: compared to DAO & RDO
- Enhanced performance by recordset object : indexing
- Recordset persistence: RecSet data can be saved in a file
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ActiveX Data Objects (ADO)…
To access ADO, VB 6.0 includes version 2.0
- a reference to the ADO object library must be included
1. Connection object
- represents an open connection to the data source
- a unique session with a datasource
Collections, properties, and methods of Conn obj
- configure a connection with a connectionString and mode properties
- specify an OLE DB provider
- open and then close connection
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ActiveX Data Objects (ADO)…2. Command object
- used to query DB and return records in a recSet obj.
- execute an operation
- manipulate the structure of a DB
Command object helps
- define the executable text of the command using commandTextproperty
- execute a command and return results using execute()
- specify type of commands. adCmdText, adCmdTable
- manage transaction using BeginTrans, commit, RollbacTr
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ActiveX Data Objects (ADO)…
3. The error object
- ADO objects can generate one or more errors
- these errors are normally contained in error object
Error object contains
- descriptions of an error
- error code/number
- source: an object that raised an error
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ActiveX Data Objects (ADO)…
4. Field object
- recordset object contains fields collection
- each field object corresponds to a column in a recSet
Field objects allow to get
- name of a field
- or change field’s data using value property
- field’s characteristics: type, definedSize, etc
5. Parameter object: arguments associated with command object
- such as in WHERE and SORT BY clause
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ActiveX Data Objects (ADO)…
6. RecordSet object
- represents entire set of records from a base table (user-input too)
- at any time, a recordset object refers to ONLY a single record
within a set of current record
- RecordCount()
- MaxRecords property
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Brainstorming
Compare ADO and DAO by
– examining the similarity of the objects, properties, and methods
they have in common
– Looking at the gap in number of objects; why such gap arises,
and how it is compensated in ADO.
Next
– Connecting to DB using ADO Data control and Using Code
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