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Database descarga (3) - Coggle Diagram

- - - - In general, a DBMS provides the following services:
        
        It allows the definition of the database by means of the data definition language. This language allows specifying the structure and type of the data, as well as the restrictions on the data. All this will be stored in the database.
        
        It allows the insertion, update, deletion and querying of data using the data management language. Having a language to perform queries reduces the problem of file systems, where the user has to work with a fixed set of queries, or has a large number of application programs that are costly to manage.
        
        In general, large multi-user SGBD offer all of the above features and more.
        
        SGBD are continuously evolving, trying to meet the requirements of all types of users. For example, many of today's applications need to store images, video, sound, etc. To satisfy this market, SGBD must change. As time goes by, new requirements will emerge, so SGBD will never remain static.
  - - - arose
        
        as extensions to Fortran programs that allowed shared access to data.
        
        Access methods supported by the operating system were developed (direct and sequential access)
        
        hierarchically structured databases were developed, followed somewhat later by network databases.
  - - - store large amounts of data organized according to a certain schema or "data model" that facilitates its storage, retrieval and modification.
- - - - Text: to enter character strings up to 255 characters.
        
        Memo: to enter a long text. Up to 65,535 characters.
        
        Numeric: to enter numbers. Stores 1,2,4,8 or 16 bytes.
        
        Date/Time: to enter data in date or time format.
        - Currency: to enter data in number format and with the currency sign.
        
        Autonumeric: in this type of field, Access automatically numbers the content.
        - Yes/No: logical field. This field type is only if we want a Yes/No, True/False, etc. content.
        
        OLE Object: to enter a photo, graphic, spreadsheet, sound, etc.
        
        Hyperlink: we can define a link to a Web page.
        
        Search Wizard: creates a field that allows you to choose a value from another table or from a list of values using a list box or a combo box.
- - - - Decimal Places: Allows you to specify the number of decimal places to display the numbers.
        Field type:
        Numeric and currency.
        
        Input mask:
        Allows you to control and filter the characters or values that users enter into a text box control, preventing errors and making it easier to type.
        Field type: Text, numeric, date/time, currency.
        
        Title:
        Allows you to define a default field label for a forms or report.
        Field type: All
        
        Default value: Enter a value in the field when new records are added (max. 255 characters long).
        Field type: All, except OLE and counter.
        
        Validation rule:
        Allows to write the condition that the entered data must satisfy to be accepted.
        Field type: All, except OLE and counter.
        
        Validation text:
        Defines the message text that is displayed when the data does not meet the conditions listed in the validation rule.
        Field type:
        All except OLE and counter.
- - - - In this option we define the fields or characteristics of each of the records or elements that we are going to have in our table.
        In each of the fields we specify the Name of the field with which we want it to appear reflected, the type of data to be stored and finally a small description of the field.
        
        As for the field properties the most important ones to be defined are:
        
        Field size
        
        Format
        
        Predefined value: which specifies the initial value
        
        Required: to indicate that its presence is mandatory.