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Module Operation Module operation complies with an application structure defined in the templates. This application structure may not match the appearance or structure of your application. However, you can modify the templates if you want to change the way the module operates. This is covered in the subsection Module Construction and Templates. Module Capabilities The resultant screen and logic that HP ALLBASE/4GL creates for the module allows the user to retrieve records from the file. Scanning the file allows the user to retrieve records on a first, last, next, or previous record basis. With HP ALLBASE/SQL tables, HP TurboIMAGE/iX data sets, and KSAM data files, keyed access is also provided. Keyed access allows the user to retrieve records based on full-key or partial-key reads. A full-key read retrieves a record with a value in its key field that matches the value the user entered. A partial-key read retrieves a record with a value in its key field that is equal or greater than the value the user entered.
NOTE Within this section, the term keyed files will refer to the three file types that offer keyed access: HP ALLBASE/SQL tables, HP TurboIMAGE/iX data sets, and KSAM data files. Keyed files must contain a key. Any HP ALLBASE/SQL tables, HP TurboIMAGE/iX data sets, or KSAM data files that do not contain a key field cannot be used to build a module.
Record retrieval capabilities are available in both inquiry (I type) modules and maintenance (M type) modules. In maintenance modules, the screen and logic created by the module builder also allow the user to add records, delete records, and modify existing records. The following module capabilities table summarizes the capabilities of a module, including how they are influenced by module type and file type. Table 8-1. Module Capabilities --------------------------------------------------------------------------------------------------- - - File Type - --------------------------------------------------------------------------------------------------- - - Keyed File - Serial - --------------------------------------------------------------------------------------------------- | Capabilities | Unique | Duplicate | Fixed | Variable | | | Key | Key | Length | Length | --------------------------------------------------------------------------------------------------- - File Scanning - Yes - Yes - Yes - Yes - --------------------------------------------------------------------------------------------------- - Full-Key Read - Yes - Yes - No - No - --------------------------------------------------------------------------------------------------- - Partial-Key Read - Yes - Yes - No - No - --------------------------------------------------------------------------------------------------- - Add Records - Yes - Yes - Yes - Yes - --------------------------------------------------------------------------------------------------- - Insert Records - No - Yes - No - No - --------------------------------------------------------------------------------------------------- - Modify Records - Yes - Yes - Yes - No - --------------------------------------------------------------------------------------------------- - Delete Records - Yes - Yes - No - No - --------------------------------------------------------------------------------------------------- It is important to realize that many aspects of the module builder, including the capabilities of the module, are influenced by both the type of HP ALLBASE/4GL file accessed and the module type. Another capability you can include in a module is link fields in the data screen. With link fields the user can access data from up to twenty other keyed files in addition to the main file for the module. The module can only read information from these secondary files. In maintenance and inquiry modules, this information can be displayed on the data screen. In maintenance modules, this information can also be used for data validation. Process Users access the module through a menu item. The menu item executes the main process, which initializes the access mode and displays the resultant screen. This transfers control of the application to the resultant screen. Control returns to the main process when the user presses the Commit Data function key. The process then performs the appropriate file transaction and returns control to the data screen. The process terminates when the user presses the Previous Menu function key. Data Screen In an inquiry module, all fields on the resultant screen, except the first field, are display-only. In a maintenance module, all fields from the main file are input fields on the resultant screen. Fields displaying data from secondary files are always display-only fields. The first line of the resultant screen is the banner line. It consists of the application name at the left, a screen title in the center, and the screen name at the right. The rest of the screen is used for label and field pairs. The label provides an on-screen name for the field. The first pair is the input key field and its label, and is normally separated from the remaining screen fields. When the main file is a keyed file, the user uses this field for keyed access to the main file. In resultant screens that access serial files, this label and field pair is still separate from the remaining fields. The format of the screen depends on the length, type, and number of fields placed on the screen. When creating the resultant screen, the module builder first attempts to place all the label and field pairs in one column down the center of the screen. If there are too many fields for this layout, the module builder then tries to place all the label and field pairs in two columns. Finally, if there are too many label and field pairs for a two column layout, the module builder tries to fit as many label and field pairs as possible onto the resultant screen. The tabbing sequence through the screen fields is from top left to bottom right. The cursor moves across the fields in each line from left to right, and then down to the left-hand field of the next line. Refer to Module Construction and Templates for further information on how the module builder creates the resultant screen. File Scanning File scanning is the only access method that is common to all HP ALLBASE/4GL file types. The user can use file scanning in both inquiry and maintenance modules. File scanning allows the user to select the first, next, previous, or last record from the file. All scanning is controlled with the function key sets. Four function keys are available to the user for scanning: Previous Record , Next Record , First Record , and Last Record . The function keys for scanning can be placed in one or more function key sets, depending on the file type and module type. Inquiry modules contain all the available scanning function keys in a single function key set, which is always displayed. Maintenance modules generally require two to six sets of function keys to display the available scanning keys. However, from the user's perspective, only two sets of function keys are used to display the function keys for file scanning. The first set displays the Previous Record and Next Record function keys. The second set displays the First Record and Last Record function keys. The More Keys function key in the first set, and the Main Keys function key in the second set, are used to switch between the two sets of function keys. The following table shows the scanning operations that are available for the various file types. Table 8-2. Scanning Capabilities by File Type ------------------------------------------------------------------------------------------------------ - - File Type - ------------------------------------------------------------------------------------------------------ | | HP ALLBASE/SQL | KSAM & HP | SERIAL | | | | TurboIMAGE/iX | | ------------------------------------------------------------------------------------------------------ | Scan Type | Unique | Duplicate | Unique & | Fixed | Variable | | | Key | Key | Duplicate | Length | Length | ------------------------------------------------------------------------------------------------------ - First Record - Yes - Yes - Yes - Yes - Yes - ------------------------------------------------------------------------------------------------------ - Next Record - Yes - Yes - Yes - Yes - Yes - ------------------------------------------------------------------------------------------------------ - Previous Record - Yes - No - Yes - Yes - No - ------------------------------------------------------------------------------------------------------ | Previous Key | No | Yes | No | No | No | | Value | | | | | | ------------------------------------------------------------------------------------------------------ - Last Record - Yes - No - Yes - Yes - No - ------------------------------------------------------------------------------------------------------ - Last Key Value - No - Yes - No - No - No - ------------------------------------------------------------------------------------------------------ The user can always step forward through a file, either from the current record or from the first record in the file. For keyed files, the order in which successive records are retrieved is ascending key field sequence. Records in serial files are retrieved in the physical order in which they are stored in the file, which is normally the order they are created. There is no ascending or descending key value sequence. Keyed Access Keyed access is available for keyed files, that is, HP ALLBASE/SQL tables, HP TurboIMAGE/iX data sets, and KSAM data files. Both inquiry and maintenance modules allow keyed access. Where the record layout allows unique key values, the user can use keyed access to retrieve a specific record. This is done by entering a value in the key field and pressing Return. HP ALLBASE/4GL attempts to locate and display a record with a matching key value. This is a full key read of the main file, and is available whenever the cursor is in the key field. If a record is located, the user can access records with key values adjacent to that entered by pressing the Previous Record and Next Record function keys. In a maintenance module, the user can modify the retrieved record or add a new record if no record is found. Where the record layout allows duplicate key values, keyed access retrieves only the first record with a matching value. The user then presses the Next Record function key to step through successive records with the same key value. For HP ALLBASE/SQL tables with duplicate keys allowed, the Previous Record function key is replaced with the Prev Key Value function key. When the user presses this function key, HP ALLBASE/4GL searches back through the table for the key value preceding the value displayed. It then retrieves the first record in the table with this key value. If after entering a value, the user presses the Next Record function key instead of Return, the partial key read function is invoked. This function attempts to retrieve the first record that matches or is greater than the contents of the key field. In all field types, except numerical and date, records are ordered by ASCII coding for retrieval. Maintenance Modules A maintenance module allows the user to add new records, and delete or modify existing records in the file. Each action is performed when the module is in the corresponding mode for the action. The current module mode is displayed in the label for the Mode function key, located in the bottom left corner of the screen. To change the module mode, the user presses the Mode function key until the required mode is attained. The mode indicates the type of change that will be made to the file when the user presses the Commit Data function key. HP ALLBASE/4GL automatically sets the mode based upon the previous action by the user. If required, the user can then change the mode as required to another available mode by pressing the Mode function key. Files with Unique Keys. When working with keyed files with unique keys, the module has three possible modes: add, modify, and delete. When the user first enters the resultant screen, the mode is set to add. In add mode, if the user enters a value into the key field and successfully retrieves a record, HP ALLBASE/4GL changes the mode to modify. In modify mode, if the user enters a key value that doesn't retrieve a record, HP ALLBASE/4GL changes the mode to add, holding the entered value in the key field. From modify mode, the user can toggle to delete mode if required. Delete mode remains the current mode until the user changes it. When the user presses the Mode function key, HP ALLBASE/4GL changes the mode to modify if an existing record is displayed, otherwise it changes the mode to add. Files with Duplicate Keys. When working with keyed files where duplicate keys are allowed, the module has three possible modes: add, modify, and delete. When the user first enters the resultant screen, the mode is set to add. Add mode remains the current mode until the user changes it to modify or delete mode. While in add mode, if the user presses the Commit Data function key with an existing key displayed, another record with the same key value is inserted into the file. From modify mode, if the user enters a key value that exists, HP ALLBASE/4GL retrieves the first record with that key and holds modify mode. If no record is retrieved, HP ALLBASE/4GL changes to add mode. While in modify mode, the user can change to add or delete mode. Delete mode remains the current mode until the user changes it. When the user presses the Mode function key, HP ALLBASE/4GL changes the mode to modify if an existing record is displayed, otherwise it changes the mode to add. Serial Files. When working with fixed-length serial files, the user has two available modes: add and modify. The mode is set to add when the user first enters the resultant screen. From add mode, if the user uses any of the four function keys for scanning, HP ALLBASE/4GL changes the mode to modify. The module remains in modify mode until the user changes it to add. With variable length serial files, the user has two available modes: add and review. Add is only available when the user is at the end of the file. In add mode, if the user presses the Mode , First Record, or Next Record function key, HP ALLBASE/4GL moves to the beginning of the file and changes to review mode. In review mode, if the user presses the Mode function key, HP ALLBASE/4GL moves to the end of the file and changes the mode to add. Secondary Files With module builder you can specify that a field in the resultant screen is linked to one of the following: * A key field in an indexed KSAM file record. * A key field in an HP TurboIMAGE/iX file record. * Any field in an HP ALLBASE/SQL table record. When creating the module, HP ALLBASE/4GL links this field to a secondary file. The secondary file can then be used to display additional information and to validate user data entry. Secondary File Functions. For each field in the resultant screen that is linked to a secondary file, the module builder creates an after function to retrieve the appropriate record from the secondary file. In maintenance modules, the after function can also be used to validate the data entered. If the link field is an input field, the function is executed as an after function. In addition, regardless of the field type, the function is always executed as a result of the SHOW command. Additional Information Display. After the user enters data into the link field, the after function uses that value as the key to retrieve a record from the specified secondary file. If a record cannot be retrieved, a warning message is displayed. If a record is retrieved, this data is available in the file record buffer and can be displayed on the resultant screen. Any fields displaying data from the retrieved record must appear on the screen after the link field. That is, the display fields must have a higher sequence number. Data Validation. When you specify the link between a screen field and a secondary file, you can also specify whether that field is validated against the secondary file. When validation is specified, the secondary file record must be retrieved before the user can commit data in the link field and continue entering data into further fields. If the validation fails, an error message is displayed and the field cannot be committed until the data is validated, or the field is blank. Limitations. All keyed file types can be used as secondary files. Serial files cannot be used as secondary files. If the index field for the secondary file allows duplicate values, the first record found will be retrieved. A file cannot be used more than once in a module. Therefore, the main file cannot be used as a secondary file within the same module, and a secondary file can only be linked to one screen field. The only limit to the number of fields that can be displayed from a secondary file is the number of fields that can fit on the screen. A maximum of twenty secondary files per module is allowed.