To look up an attribute for a data object, you must first
determine the type of the object and then ask for the appropriate
attribute value for that type. The functions that you can use to
query the database for data information are shown in Table 9-4 “Data-Typing Database
Query Functions” Each of these
functions has a man page in section 3. Refer to the appropriate
man page for more information.
Table 9-4 Data-Typing Database
Query Functions
Function | Description |
|---|
DtDtsBufferToAttributeList | Finds the list of data attributes for
a given buffer. |
DtDtsBufferToAttributeValue | Finds the data attribute for a given
buffer. |
DtDtsBufferToDataType | Finds the data-type name for a given
buffer. |
DtDtsDataToDataType | Finds the data type for a given set of
data. |
DtDtsDataTypeIsAction | Returns the resulting saved data type
for the directory. |
DtDtsDataTypeNames | Finds a complete list of available data
types. |
DtDtsDataTypeToAttributeList | Finds the attribute list for a given
data attribute name. |
DtDtsDataTypeToAttributeValue | Finds the attribute value for a given
data attribute name. |
DtDtsFileToAttributeList | Finds the list of data attributes for
a given file. |
DtDtsFileToAttributeValue | Finds the data attribute value for a
given file. |
DtDtsFileToDataType | Finds the data type for a given file. |
DtDtsFindAttribute | Finds the list of data types where attribute
name matches value. |
DtDtsFreeAttributeList | Frees the memory of the given attribute
list. |
DtDtsFreeAttributeValue | Frees the memory of the given attribute
value. |
DtDtsFreeDataType | Frees the application memory for the
given data-type name. |
DtDtsFreeDataTypeNames | Releases memory created with the DtDtsDataTypeNames
or DtDtsFindAttribute call. |
DtDtsIsTrue | A convenience function that converts
a string to a Boolean. |
DtDtsRelease | Unloads the data-typing database information,
generally in preparation for a reload. |
DtDtsSetDataType | Sets the data type for the specified
directory. |
DtsLoadDataTypes | Initializes and loads the database fields
for the data-typing functions. Use instead of DtDbLoad
when you do not need to use actions or action types and you need
extra performance. Use DtDbLoad
when you need to use actions. |
You can type data and retrieve attributes in one of three
ways: simple, intermediate, or advanced.
Simple Data Typing |
 |
The simplest way to type data is to use the following functions:
DtDtsFileToAttributeValue
When you use these functions, a file is typed and a single
attribute, or the entire list, is retrieved. System calls are made,
data is typed, and the attribute is retrieved. These functions call
the intermediate data-typing functions.
DtDtsBufferToAttributeList
DtDtsBufferToAttributeValue
Buffers are assumed to have a mode that matches regular files
that have read/write permissions. See “Advanced
Data Typing” to type read-only buffers.
Intermediate Data Typing |
|
When you type data and retrieve attributes, the data-typing
part of the process is the most expensive in terms of performance.
You can type data in a second way that improves performance by separating
the data-typing and attribute- retrieval functions. Use the following
functions for intermediate data typing:
DtDtsDataTypeToAttributeList
DtDtsDataTypeToAttributeValue
Use these functions if your application queries for more than
a single attribute value. When you use these functions, an object
is typed and then that type is used to retrieve one or more attributes
from the attribute list.
Using the intermediate data-typing functions is the recommended
way to type data and retrieve attributes. These functions call the
advanced data-typing functions and make the same assumptions about
buffers as the simpler data typing.
Advanced
Data Typing |
|
Advanced data typing separates system calls, data typing,
and attribute retrieval even further. Advanced data typing is more
complicated to code because it uses data from existing system calls,
which are initialized in advance and are not included as part of
the data-typing function. Use the following function for advanced
data typing:
DtDtsDataToDataType
To type a read-only buffer, a stat
structure should be passed that has the st_mode
field set to S_IFREG | S_IROTH | S_IRGRP | S_IRUSR.
Data Types That Are Actions
(DtDtsDataTypeIsAction) |
|
For every action in a database a synthetic data
type is generated when a database is loaded that allows
actions to be typed. These data types may have two additional attributes:
IS_ACTION
is a string-Boolean value that tells users of this data type that
it is an action. If IS_ACTION
is set to the string true (independent
of case), the data is an action.
IS_SYNTHETIC
is a string-Boolean value that tells users of this data type that
it was generated from an entry in the ACTION
table. If IS_SYNTHETIC is
set to true, the data type
was generated.
Printable version
