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ACCESS

 

The ACCESS section of a GPD declares how the concept values are associated with the underlying database, i.e. which ``physical'' database object a ``logical'' concept refers to and where to find it in the database --- the path to the parts of the view. Therefore, for each subpart listed in STRUCTURE section, you declare how to find that part in the database.

In order to make it easier to understand the examples in this section, we now introduce a set of GPD language keywords and some specialized syntax, an understanding of which will help in following the discussion.

In the following section, we will discuss the kinds of access that can be made to database objects and give examples. Please refer to these examples as the discussion progresses.

Keep in mind that each information component is made up of attributes, links and an image. Figure 7.12 shows such an information component.

 


:  Parts of an `information component'

Attributes and links are named using the group name, the field name, and for links, the position. For example, a link might be named by TEXT:Paragraph:1, meaning group TEXT, field Paragraph, position 1 (positions begin at 1). An attribute value might look like TEXT:Title, meaning the TEXT attribute group and Title field under that group. There can only be one attribute of this name in a given information component.

Presently, one can refer to the following database concepts:

  1. All attribute groups in an information component

    For example, the example in figure 7.13 would retrieve all attribute groups and display the attribute group names.

     


    :  ACCESS of all attribute groups

    Again, ATTR is a keyword.

  2. All fields within a certain attribute group in an object

     


    :  ACCESS of attribute fields

  3. The value of a certain field within a certain attribute group

    In the example in figure 7.20, we again see that all attribute groups are retrieved using ATTR. The fields are then retrieved using the value of the parent (the attribute group name) as ATTR ``%VALUE%''. For each field, the value is retrieved using the group name in the parent (``%GROUP%'') and the value of the parent (the field name). Thus, if there is a group SYSTEM with a field Created, the access for the value will be ATTR SYSTEM Created.

     


    :  ACCESS of attribute values

  4. All link groups in an object

    This functions in the same way as showing all attribute groups in an object, but rather than the keyword `ATTR', you use the keyword `LINK'.

  5. All fields within a certain link group in an object

    Again, this is the same as for attribute fields but with the keyword LINK rather than ATTR.

  6. All items for a field within a certain link group in an object

    As with the previous two items, this works in a similar fashion as all the fields in an attribute group, but using LINK instead of ATTR.

  7. The first item for a field with a certain link group in an object

    This is a special case which is seldomly used. Instead of the ACCESS directive `LINK GROUP Name' (which would pick up all the link items in this link group), you use `LINK GROUP Name 1', which specifies that you use the first link item in that link group. No other integer other than 1 is acceptable.

    This is available simply so that you can view singular link items even if there are multiple link items in that link group.

  8. The image of an object

    This is accessed using the keyword IMAGE. Figure 7.21 shows the `image' GPD, which does this.

     


    :  The `image' GPD





next up previous contents index
Next: Notes about the Up: GPD Language Previous: STRUCTURE



Martin Sjolin
Mon May 29 19:53:45 MET DST 1995