HP 3000 Manuals HP 3000 Manuals
Chapter 4 The Loading Process Schema Generation Process This chapter describes how SDDBC creates the schema based on definitions in the System Dictionary. The description is organized in a fashion that follows the overall schema structure. If you are not familiar with schema structure, refer to the section in the Turbo IMAGE/V Reference Manual (32215-90050) entitled "Defining a Database." Database SDDBC searches the IMAGE-DATABASE entity for the database specified in the IMAGE command. This entity is used as the database name in the schema. The attribute value of image-database-type is used to determine if the database is a TurboIMAGE database. Passwords To get the user classes and passwords for the database, SDDBC searches the IMAGE-DATABASE contains IMAGE-CLASS relationships. The user class numbers and passwords are obtained from the attributes class-number and password of the image-class entity. SDDBC sorts the password information by class-number and writes the user class numbers and passwords to the password part of the schema file. Items To get all the items in the database, SDDBC first searches all the data sets related to the specified database by finding the IMAGE-DATABASE contains IMAGE-DATASET relationships. The record layout of the IMAGE-DATASET is then found by using the IMAGE-DATASET contains RECORD relationships. There can be more than one record layout per data set. If there is more than one layout for the data set, SDDBC uses the primary record layout which is indicated by the IMAGE-DATASET contains RECORD attribute primary-record. If there is more than one record layout and none of them are the primary record layout, then SDDBC will use the first record layout as retrieved from the dictionary. If there is more than one primary record layout, SDDBC will use the first primary record as retrieved from the dictionary. The items are obtained by following the RECORD contains ELEMENT relationships. The attribute element-type of the RECORD contains ELEMENT relationship is used as the type designator of an item definition. If the attribute back-reference is true, then the element-type attribute is retrieved from the element entity itself. The element entities are then retrieved, and attribute count is used as sub-item count, and attribute byte-length is used to derive the sub-item length as follows: Item type Byte-length Sub-item length D,I,J,K,R n n + 1 / 2 U,X,Z n n P n 2 * n The sub-item length of the data item is rounded to an integral number of words in length regardless of the type designator and its unit of measure. This is to conform with the standards set by IMAGE/V. To get the read and write class lists for an item definition, SDDBC searches the ELEMENT contains IMAGE-CLASS relationships. The class list is appended next to the data item in the item part of an item definition. SDDBC then writes all the data items in sorted order (of item names) to the item part of the schema file. Data Sets SDDBC gets the data sets and all related data items within each data set from System Dictionary as described previously under "Items" . Based upon the ORDER option, the data sets are generated in the order of either AUTOMATIC, MANUAL, and DETAIL, or in the order of retrieval. If data sets are generated by set type order, within each type they are generated in the order they were retrieved. The order of the items in the data set is determined by the relationship-position attribute in the RECORD contains ELEMENT relationship. The search item, master set name and sort item name of a DETAIL data set is obtained from five-way chain relationships image-dataset, element, element, image-dataset, image-database. The attribute primary-flag in this chain relationship indicates whether it is a primary path or not. Through this chain relationship, the path count for the search item in MASTER sets is also obtained. The search item of a MANUAL master set is identified by the image-dataset key element relationship. To get the read and write class lists for each data set, SDDBC searches the IMAGE-DATASET contains IMAGE-CLASS relationships. The class list is appended next to the data set name in the set part of the schema. SDDBC supports TurboIMAGE creations by generating the device class if defined in the dictionary for the data set header line. This information is retrieved from the IMAGE-DATASET uses DEVICE-CLASS relationship. The capacity of a data set is obtained from the attribute capacity of IMAGE-DATABASE contains IMAGE-DATASET.