The MS Access database management system (DBMS) is a relational database management system operating in Windows environment XP. It provides everything necessary funds to define, process, and manage data when working with large volumes of information. The DBMS allows you to create applications that run in the Windows environment and fully meet the customer's needs.
The DBMS includes tools for managing tables, queries, forms, reports, macros and modules as independent objects stored in one database file (extension .mdb). This makes creating related objects and checking data integrity much easier.
Let's briefly look at the composition of the database file and the architecture of the DBMS.
The DBMS calls everything that can have a name objects. In an Access database, the main objects are tables, queries, forms, reports, macros and modules.
Table is an object defined to store data. Each table includes information about a real-world object, such as a firm's clients. A table consists of a header and a body. The header includes the object attribute names (columns) and their properties, such as the customer's last name, phone number, and address. The body contains tuples (rows), each row representing a set of column values that store data about a particular object instance. For example, customer information:
Semenov; 75-48-09; Ryazan, st. Polevaya, 20.
For each table you can define primary key, which ensures that each row is unique, one or more indexes that ensure the ordering of records, and other properties.
When working with Access, tables are one of the main objects; all other elements, such as forms, queries and reports, are built on their basis. The table collects data on a specific topic, for example, all information about the company’s clientele. Each row of data in the customer table contains information about a specific customer. This information may be heterogeneous, and therefore the line consists of several different types of fields containing the client’s last name, telephone number, address, account number, etc.
An Access database can consist of several tables, each of which stores information on one topic. One table can store information about clients, another - about all trade agreements that have been concluded with certain clients, the third - information about expenses, taxes and expenses for the development of the company, the fourth - an inventory list of the warehouse fund, the fifth - timing of exhibitions and presentations, etc.
Request is an object that allows the user to obtain the desired data from one or more base tables and other queries. In a query, you can specify conditions that the data must satisfy. Thanks to this, the query allows you to extract only the necessary data from a large array of information stored in the database. To create a request, use a sample request (QBE) or instructions SQL. You can create queries to select, update, delete, or add data. Using queries, you can create new tables using data from one or more tables that already exist.
Form is an object designed primarily for entering data, displaying it on the screen, or controlling the operation of an application. Forms are used to implement customer requirements for presenting data from tables and queries. The forms can be printed. Using a form, you can launch in response to some event macro or procedure performing certain data processing.
Report is an object designed to create a document that can later be printed or included in a document in another application. Before printing the report to the printer, you can view it on the screen.
Macro is an object that represents a structured description of one or more actions that will be performed in response to a specific event. For example, you can define a macro that, in response to selecting an element on the main form, opens another form. Using another macro, you can check the value of a field when its contents change. You can run another macro or module function from one macro.
Module is an object containing programs for Microsoft Access Visual Basic, which can be developed by the user to implement non-standard procedures when creating an application.
The original Access window is simple and uncluttered. The six tabs in this window represent the six objects the program works with.
Tables- main database objects. They store data. A relational database can have many interconnected tables.
Requests– these are special structures designed to process database data. With the help of queries, data is organized, filtered, selected, modified, combined (i.e. processed).
Forms– these are objects with the help of which new data is entered into the database and existing data is viewed.
Reports– these are forms “on the contrary”. With their help, data is sent to the printer in a convenient and visual form.
Macros These are macro commands. If some operations with the database are performed frequently, it makes sense to group them into one macro and assign it to a dedicated key combination.
Modules are software procedures written in Visual Basic. If standard Access tools are not enough to satisfy particularly sophisticated customer requirements, the programmer can expand the capabilities of the system by writing the necessary modules for this.
Modes of working with Access.
From an organizational point of view, there are two different modes when working with any database: design And operational(custom). The creator of the database has the right to create new objects in it (for example, tables), set their structure, change the properties of fields, and establish the necessary connections. It works with the database structure and has full access to the database. One database may have one, two or several developers.
A database user is a person who fills it with information using forms, processes data using queries, and receives results in the form of resulting tables or reports. One database can have millions of users, and, of course, access to the database structure is closed to them.
The starting window of the database structure has six tabs for the main objects and three command buttons: Open, Designer, Create. With their help, the mode of working with the database is selected.
The Open button opens the selected item. If this is a table, then you can make changes to it, view it, etc.
The Design button opens the selected object, but in a different way. It opens its structure and allows you to edit not the content, but the device. If this is a table, then you can enter new fields into it or change the properties of existing fields. If it's a form, you can modify or create controls. Obviously, this mode is not for users of the database, but for its developers.
The Create button serves to create new objects. This control is also intended for database designers. Tables, queries, forms, reports can be created in several different ways: automatically, manually or using the Wizard.
Tables. Creating tables.
Tables are the main objects of the database. You can do without queries, forms, reports, etc., but if there are no tables, then there is no database.
Creating a table consists of specifying its fields and assigning their properties. It starts by clicking the Create button in the Database window. There are several ways to create a new table, differing in the level of automation.
Importing tables from another database. Depending on the circumstances, the imported table may contain the structure of the fields, their names and properties, as well as the contents of the database. If we're talking about about someone else's table, which is located on a remote server and which cannot be imported in its entirety, use the Link to tables mode. This is similar to connecting to a table to share its data.
Experienced developers use the Table Wizard. This is a program that speeds up the creation of a table structure. The wizard asks a series of questions and, based on the answers received, creates the table structure automatically. Despite the fact that this mode serves to simplify the work, it is not recommended for beginners to use it, since without knowing all the terminology, it is easy to get confused in the questions and answers. You should try creating your first tables manually.
The Operating mode item opens a template in which all fields have formal names: Field 1, Field 2... etc. and one standard text type. Such a table can be filled with information immediately.
The most universal manual method is provided by the Constructor item. In this mode, you can independently set field names, select their type, and configure properties.
The data the DBMS works with is arranged in a hierarchical sequence. At the top level are the main MS Access objects; tables, forms, queries, reports, macros and modules.
Table- This is the main type of objects. All others are derived from the table. The data elements that make up a table are records and fields. Tables store data and display all records and fields, and tables also store established relationships. Before creating a database in Access, you need to develop structure of database tables and establish connections between them.
Table structure- this is a description of the order of fields, their types, sizes, names and other characteristics.
Record - the sequence of values described in the structure.
Field - a record element containing information about one property of an object and characterized by the following parameters:
Field name (written without spaces - like a variable name);
Field value type (text, numeric, logical, date-time, MEMO;
Field size (depends on the type of possible values);
Field value (corresponds to a specific record).
A field whose values are not repeated is called key .
When developing a table structure, you should avoid repeating the same records multiple times (redundancy). For this purpose, it is necessary to change the structure of the table, reducing its volume by splitting it into several interrelated tables. This process is called normalization(optimization) of the data model.
Table structure in a multi-table database, it must be created in such a way that a connection can be established between them, i.e. tables must contain general fields, identical in type and format of stored data.
Data Schema- description of the structure of relationships in a multi-table database.
Forms- these are customizable dialog boxes, stored in the database as objects of a special type. Used to view, enter and edit one table record. Forms may contain controls, with the help of which data in tables is accessed: text fields for entering and editing data, buttons, checkboxes, switches, lists, labels, as well as object frames for displaying graphics and OLE objects.
Tables And Forms - these are the modes used to create and view a database.
Actions performed on information stored in a database are called data manipulation (data processing). These include selecting data according to certain conditions, sorting data, updating, deleting and adding data. These actions are performed using queries.
Request is a command to perform a certain type of data manipulation. Designed to filter and select records stored in a table and satisfying certain conditions. Selection conditions - these are restrictions that the user places on the request.
Report is an object designed to analyze data and output it to a file, text document or on the screen using a created template - a sample report.
Macros are means program control data. They are a set of commands for automatic execution some operations.
End of work -
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As can be seen from Fig. 3.4 and 3.5, base Access data can have the following objects: tables, forms, queries, reports, pages. In addition, skilled users can also work with macros and modules. Macro is a set of special macro commands (for example, Open Form, Print Report etc.), and module is a program written in Access Basic or Visual Basic for Applications.
Fig.3.5. Access objects
Table– a basic MS Access object containing data. All other objects are derived and are created only on the basis of prepared tables.
A form is not a standalone Access object: it simply helps you enter, view, and modify information in a table or query. Form is an object designed for convenient data entry and display. Unlike tables, forms do not contain database information. A form is just a format (form) for displaying data on a computer screen. Forms can be built on the basis of tables and queries. Building forms based on queries allows you to present information from several tables.
Queries and reports perform independent functions: select, group, present, and print information. Request is a tool for analyzing, selecting and changing data. A query is an instruction for selecting the required records from a given database in accordance with certain conditions. Essentially, a query is a question that a user asks Access about information stored in the database.
Report is an object designed to create a document that presents information in the form required by the user, and which can subsequently be printed.
Pages data access are a special type of Web pages designed for viewing and working via the Internet or intranet with data stored in the database Microsoft data Access or Microsoft SQL Server. Using the page, users can enter, edit and delete data from the database.
Every MS Access object has a name. The name must be no more than 64 characters and can include any combination of letters, numbers, spaces, and special characters except for the point exclamation mark and square brackets. The name must not begin with a space character, must not include control characters (ASCII codes 0 to 31), and must not include straight quotation marks in table names.
Work with each database object is performed in a separate window, and two modes of operation are provided:
ü operational mode– the mode in which information is viewed, changed or selected;
ü design mode– the mode in which the layout and structure of an object (for example, table structure) is created or changed.
In addition, the database file includes another document that has its own window: data diagram . Data Schema– This is the window in which relationships between tables are created, viewed, modified, and broken. These connections help you control data and create queries and reports. If you select the command Service Data Schema...(or click the corresponding toolbar button), a document window will appear on the screen Data schema.
The database window has three command buttons ( Open, Constructor And Create) and seven tabs (according to the number of Access objects): Table, Query, Form, Report,Pages, Macro and Module(see Fig. 3.4) . If any tab is selected, its window displays a list of existing objects of this type in this database.
For example, if you select the tab Table, then the window displays a list of tables in the open database (Fig. 3.6). To open a table, select its name in the list and click the button Open. To include in the database new table, you have to press the button Create. To correct the layout of an existing table, select its name in the list and click the button Constructor.
Rice. 3.6. Tab Tables
The same operations are performed on all other Access database objects.
The set of horizontal menu items and the composition of toolbars depend on the type and mode of the document window, which is in at the moment actively. For example, a table window in online mode has buttons Cut, Sort ascending etc. (Fig. 3.7), and in design mode - buttons Properties, Define Key etc. Working with toolbars follows the Windows standard.
Rice. 3.7. In the database window, the table window is active in operational mode
Access are elements that store information and are used to automate actions with it.
Basic Access database objects
Let's list the main objects.
- Tables are the main elements of a database, without which it cannot exist. They are where the data is contained.
- Forms are an interface display of tables; these are windows in which database users work.
- Queries are used to retrieve data, write and change information, and delete existing table elements.
- Reports provide data in the form and structure that users need, with summaries and statistics collection.
- Macros are database program units. Their task is to perform the necessary actions when certain events occur.
- Modules are Access database objects. They react to changes occurring in the database or perform independent tasks.
Tables
Database tables are the basic elements in which information is stored. In relational databases, tables are called relationships. They consist of rows and columns. The rows are called records, and each row contains information related to one element. The columns contain table parameters. The columns are called database fields.
Database development begins with creating tables. Attributes are specified for it - properties that determine behavior. For the basic object in Access - “Tables” - table properties are defined in design mode on the right side of the screen. Here you set the main and subordinate fields, the default orientation and mode, define the description, etc.
At the bottom of the screen you set properties for each field. The set of parameters varies depending on the Here you set the general properties of the column and specify the substitution for fields of numeric or text types: list or combo box. Parameters for substitution are also indicated here: data source, title, format, availability of changes, etc.
There are relationships between tables defined by keys - fields of one relationship that are referenced by the values of another. Keys are columns with unique values in them to uniquely identify a record.
Forms
Forms are objects in Access that are used to make the user experience more convenient. Tabular display of information is not always convenient and clear, so forms are created that allow you to enter and change data.
Control elements are placed on the form: buttons, drop-down lists, text fields, checkboxes, attachments, pictures, and others. Tools on the control panel allow you to enter a company logo, date and time, and title. You can develop a form in “Design” mode, “Layout” mode and, in fact, in “Forms” mode.
In the structure of the customer table in the figure above, we see 7 fields: “Code”, “Name”, “Middle name”, “Last name”, “Date of birth”, “Gender” and “Age”. But the “Code” field is technical, cannot be changed and is not needed to demonstrate it to the user of the database. Therefore, it is removed from the form, leaving only those fields whose values need to be added or changed.
The properties of the form and each of the displayed fields - Access form objects - are located on the right. Here you set what the data editing window looks like (the “Layout” tab), where to get the data for display (the “Data” tab), what actions to perform when individual events occur (the “Events” tab) and other properties.
Requests
Queries are used for various manipulations with data in Access. The most popular queries are to retrieve data. They make it possible to obtain field values from tables that meet specified conditions and display them in the required form with the necessary sorting and grouping of rows.
These objects in Access are created using the “Designer”. The developer selects the fields needed for viewing, sorting, and specifies the conditions for selecting records. The request properties are displayed in the window on the right. Here it is defined appearance selection results and parameters such as blocking records when executing a request, a filter when loading, a data source, response timeout, etc.
Queries are also used to add and change existing records, as well as delete rows that meet specified conditions.
Reports
Reports are objects in Access required to display information from tables into printed forms. Reporting forms are created by a wizard or in Design mode. To do this, select a data source for generating printed form. Fields in the report can be grouped and sorted, and results can be displayed.
It is also possible to create forms of contracts and agreements using a pre-created document template. Table fields are inserted into the finished form, the necessary page elements are added: number, footers, header, logo, etc.
The report properties are indicated in the window on the right. The properties of individual printed form objects are also set there: headers, controls, data areas, etc.
This is what the finished template report looks like:
Macros
Another of the main objects of Access are macros. They represent a sequence of actions that need to be performed when a certain event occurs. Macros are created using the “Constructor” and macro commands for various purposes provided by the system.
Macro commands are intended for importing and exporting data, working with other database objects, setting filters and processing table records, etc. The example below shows adding simple macro, which is launched when you click on the “Cancel” button of the “Clients” form. Its purpose is to simply close the form without saving the information entered into it.
Modules
Modules are objects in Access that represent procedures and functions used to react to events in the database or for calculations. They are developed using VBA - Visual Basic for Application code. This is a special language for writing code in Microsoft programs Office - Access, Word and Excel.
For the customer form, we’ll make the “Age” field calculated. To do this, in the “Design” mode of the form, select the required field and select the procedure for processing the “Gaining Focus” event in the properties window on the “Events” tab.
Let's write a processing module:
Private Sub Age_GotFocus()
Age.Value = DateDiff("yyyy", [Date of Birth], Date)
Now, when you navigate between records and focus on the “Age” field, the value of this field is calculated automatically.
It should be understood that a table key, for example, is not an Access object, even though it is used to store information. A key is part of a table, and not an independent element of the database.
The information provided in this article will help you understand what database objects are, what properties they have and what functions they perform.
