# Accessing the Data-Typing Database

This chapter describes the data-typing functions and how to use the data- typing database.

PG.datat.mkr.2
PG.datat.mkr.5
PG.datat.mkr.9
PG.datat.mkr.12
PG.datat.mkr.14

## Summary

Data typing provides an extension to the attributes of files and data beyond what is provided by the traditional UNIX file systems. These extensions consist of attributes, such as icon names, descriptions, and actions, that can be performed on files and data. This information is stored in name/value pairs in the `DATA_ATTRIBUTES` table (or database). The desktop uses a certain set of `DATA_ATTRIBUTES`, described in the following paragraphs. The `DATA_ATTRIBUTES` table is extendable for future and application-specific growth, although extending this table is not recommended because other applications may not check the additions.

Data is matched with a specific file or data entry in a `DATA_CRITERIA` table. The `DATA_CRITERIA` table entries are sorted in decreasing order from most specific to least specific. For example, `/usr/lib/lib*` is more specific than `/usr/*` and would, therefore, appear first. When a request to type a file or data is made, the table is checked in sequence to find the best match using the information provided either from the file or from the data. When an information and entry match is found, `DATA_ATTRIBUTES_NAME` is used to find the proper `DATA_ATTRIBUTES` entry.

### Library and Header Files

To use data typing, you need to link to the `libDtSvc` library. Actions are usually loaded with the data-typing information. Actions require links to the `libXm` and `libX11` libraries. The header files are `Dt/Dts.h` and `Dt/Dt.h`.

### Demo Program

A demo program containing an example of how to use the data-typing database is in `/usr/dt/examples/dtdts/datatypes/datatyping.c`.

## Data Criteria and Data Attributes

Data typing consists of two parts:

- A database that stores data criteria and data attributes

- A collection of routines that query the database

The attributes of
data criteria, in alphabetical order, are:

- `CONTENT`

- `DATA_ATTRIBUTES_NAME`

- `LINK_NAME`

- `LINK_PATH`

- `MODE`

- `NAME_PATTERN`

- `PATH_PATTERN`

PG.datat.mkr.7 describes the data criteria in the order in which you are most likely to use them.

## Data Criteria in Order of Most Likely Use

`Criteria` | `Description` | `Typical Usage`
`DATA_ATTRIBUTES_NAME` | The name of this type of data. This value is a `record_name` in the data attributes table. | POSTSCRIPT
`NAME_PATTERN` | A shell pattern-matching expression describing the file names that could match this data. The default is an empty string, which means to ignore file patterns in matching. | `*.ps`
`CONTENT` | Three values that are interpreted as the start, type, and value fields of the magic file used by the file utility. See the `file`(1) man page for more information. The default is an empty field, which means to ignore contents in matching. The following types are examples of what can be matched: string, byte, short, long, and file name. | `0 string !%`
`MODE` | A string of zero to four characters that match the mode field of a `stat` structure. See the `stat(2)` man page for more information. The first character indicates: `d` matches a directory `s` matches a socket `l` matches a symbolic link `f` matches a regular file `b` matches a block file `c` matches a character special file | `f&!x`
| The characters listed below can be either the first or subsequent characters: `r` matches any file with any of its user, group, or other read permission bits set. `w` matches any file with any of its user, group, or other write permission bits set. `x` matches any file with any of its user, group, or other execute or directory-search permission bits set. |
| For example, the `MODE` field of `frw` matches any regular file that is readable or writable; `x` matches any file with any of its executable or search bits set. The default is an empty field, which means to ignore the mode in matching. |
`PATH_PATTERN` | A shell pattern-matching expression describing the absolute path names that could match this data. The default is an empty string, which means to ignore path patterns in matching. | */mysubdir/*
`LINK_NAME` | See `dtdtsfile(4)` man page. |
`LINK_PATH` | See `dtdtsfile(4)` man page. |

Some of the more common attributes of data types, in alphabetical order, are:

- `ACTIONS`

- `COPY_TO_ACTION`

- `DESCRIPTION`

- `ICON`

- `INSTANCE_ICON`

- IS_EXECUTABLE

- `IS_TEXT`

- `LINK_TO_ACTION`

- `MEDIA`

- `MIME_TYPE`

- `MOVE_TO_ACTION`

- NAME_TEMPLATE

- `PROPERTIES`

- `X400_TYPE`

PG.datat.mkr.6 describes the data attributes in the order in which you are most likely to use them.

## Data Attributes in Order of Most Likely Use

`Criteria` | `Description` | `Typical Usage`
`DESCRIPTION` | A human-readable description of this data. If this field is `NULL` or is not included in the data attribute record, the name of the data attribute should be used. | This is a PostScript page description.
`ICON` | The name of the icon to be used for this data. If this field is `NULL` or is not included in the data attribute record, the standard icon should be used. See `dtdtsfile(4)` for more details on icon naming. | `Dtps`
`PROPERTIES` | Keywords to indicate properties for this data. Valid values are invisible and visible. If this field is `NULL` or is not included in the data attribute record, the visible property should be assumed. Use this if you want to completely hide files from the user. | `invisible`
`ACTIONS` | A list of actions that can be performed on this data. This list refers to names in the action table for actions that are to be presented to the user for objects of this type. If this field is `NULL` or is not included in the data attribute record, no action is available. | `Open,Print`
`NAME_TEMPLATE Field` | A string used to create a new file for data of this type. The string is passed to `sprintf`(3) with the file name as the single argument. The default is empty. Contrast this field with the `NAME_PATTERN` field of the data criteria table in that the template is used to create a specific file, such as `%s.c`, whereas the pattern is used to find files, such as `*.c`. | `%s.ps`
`IS_EXECUTABLE Field` | A string-Boolean value that tells users of this data type that it can be executed as an application. If `IS_EXECUTABLE` is set to `true` `(`see `DtDtsIsTrue()`) the data is executable. If this field is `NULL`, is not included in the data attribute record, or is not set to true, then the data is considered not executable. | `true`
`MOVE_TO_ACTION` | The name of an action to be invoked when an object is moved to the current object. | `FILESYSTEM_MOVE`
`COPY_TO_ACTION` | The name of an action to be invoked when an object is copied to the current object. | `FILESYSTEM_COPY`
`LINK_TO_ACTION` | The name of an action to be invoked when an object is linked to the current object. | `FILESYSTEM_LINK`
IS_TEXT | A string-Boolean value that tells users of this data type that it is suitable for manipulation (viewing or editing) in a text editor or text widget. The `IS_TEXT` field is set to `true` `(`see `DtDtsIsTrue()`) if the data is textual in nature and if it should be presented to the user in text form. Criteria for making this determination include whether data consists of human language, is generated and maintained manually, is usefully viewable and editable in a text editor, or contains no (or only minimal) structuring and formatting information. | See PG.datat.mkr.8 for more examples.
| If the `IS_TEXT` field is `true`, the data is eligible to be displayed directly by an application. That is, the application can load the data directly into a text editing widget, such as `XmText`. |
MEDIA Field | The names in the `MEDIA` name space describe the form of the data itself. `MEDIA` names are used as ICCCM selection targets, named in the `MEDIA` field of the data-type records, and used in the type parameter of ToolTalk Media Exchange messages. The `MEDIA` name space is a subset of the name space of selection target atoms as defined by the ICCCM. All selection targets that specify a data format are valid `MEDIA` names, and all valid `MEDIA` names can be used directly as selection targets. Some selection targets specify an attribute of the selection (for example, `LIST_LENGTH`) or a side effect to occur (for example, `DELETE`), rather than a data format. These attribute selection targets are not part of the `MEDIA` name space. | `POSTSCRIPT`
`MIME_TYPE` | `MEDIA` is the desktop internal, unique name for data types. However, other external naming authorities have also established name spaces. Multipurpose Internet Message Extensions (MIME), as described in the referenced MIME RFC, is one of those external registries, and is the standard-type name space for the desktop mailer. | `application/postscript`
`X400_TYPE` | X.400 types are similar in structure to the `MEDIA` type, but are formatted using different rules and have different naming authorities. | `1 2 840 113556 3 2 850`
`INSTANCE_ICON Field` | The name of the icon to be used for this instance of data, typically a value such as `%`name`%.icon` [Bug in `dtdtsfile(4)` man page, too.] If `INSTANCE_ICON` is set, the application should use it instead of `ICON`. If this field is `NULL` or is not included in the data attribute record, the `ICON` field should be used. | `/`myicondir`/%`name`%.`bm
`DATA_HOST` | The `DATA_HOST` attribute is not a field that can be added to the data attributes table in the `*.dt` file, but it may be returned to an application reading attributes from the table. The data-typing service adds this attribute automatically to indicate the host system from which the data type was loaded. If this field is `NULL` or is not included in the data attribute record, the data type was loaded from the local system. |

The `IS_TEXT` field differs from the text attribute of the `MIME_TYPE` field, which is the `MIME` content type, as described in the referenced `MIME_ RFC`. The `MIME` content type determines whether the data consists of textual characters or byte values. If the data consists of textual characters, and the data is labeled as `text/*`, the `IS_TEXT` field determines whether it is appropriate for the data to be presented to users in textual form.

PG.datat.mkr.8 shows some examples of `IS_TEXT` usage with different `MIME_TYPE` attributes.

## IS_TEXT Attribute Examples

`Description and MIME_TYPE Attribute` | `IS_TEXT Value`
Human language encoded in ASCII with `MIME_TYPE text/plain` | `IS_TEXT true`
Human language encoded in E*UC, JIS, Unicode, or an ISO Latin charset with `MIME_TYPE text/plain; charset=XXX` | `IS_TEXT true`
CalendarAppointmentAttrs with a `MIME_TYPE text/plain` | `IS_TEXT false`
HyperText Markup Language (HTML) with a `MIME_TYPE text/html` | `IS_TEXT true`
PostScript with `MIME_TYPE application/postscript` | `IS_TEXT false`
C program source (`C_SRC`) with `MIME_TYPE text/plain` | `IS_TEXT true`
Bitmaps and pixmaps (`XBM` and `XPM`) with `MIME_TYPE text/plain` | `IS_TEXT false`
Project or module files for the desktop application building service with `MIME_TYPE text/plain` | `IS_TEXT false`
Shell scripts with `MIME_TYPE text/plain` | `IS_TEXT false`
Encoded text produced by `uuencode`(1) with `MIME_TYPE text/plain` | `IS_TEXT false`
*`MIME_TYPE text/plain` | `IS_TEXT false`

See the `dtdtsfile(4)` man page for more information about data-type attributes.

## Data-Typing Functions

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 PG.datat.mkr.10. Each of these functions has a man page in section 3. Refer to the appropriate man page for more information.

## 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:

- `DtDtsFileToAttributeList`

- `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 PG.datat.mkr.11 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:

- `DtDtsBufferToDataType`

- `DtDtsFileToDataType`

- `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.

## Registering Objects as Drop Zones

If your application defines data types, follow these steps to ensure that it provides all the drag and drop behavior that you intend:

1. In your application, decide if you need to define any data types.

2. For each data type you define, decide whether you want the associated object to be a drop zone.

3. For each object that you want to register as a drop zone, decide which operations—move, copy, or link—you want to define.

4. For the drop operations that are valid for each object, define the appropriate drop actions (set the `MOVE_TO_ACTION`, `COPY_TO_ACTION`, and `LINK_TO_ACTION` attributes).

If your application displays icons for data objects, you may choose to support those icons as drop zones. If so, you need to query the `MOVE_TO_ACTION`, `COPY_TO_ACTION`, or `LINK_TO_ACTION` attributes to determine the drop behavior for those data objects. Objects should support drop operations only if the corresponding attribute value is not `NULL`. If all three attributes have `NULL` values, the object should not be registered as a drop site. Whenever you set at least one of these attributes for an object with a defined data type, your application registers that object as a drop zone.

When a user drags an object to a drop zone, your application determines which gesture (that is, which drag operation) was used to make the drop. Based on the drag operation and the drop zone's data type, the application retrieves a drop attribute from the data-typing database. It then calls `DtActionInvoke`, using the following two rules to determine its parameters:

1. If the user drops objects A and B onto object C, call `DtActionInvoke` with C, A and B as args. The `action` is the value of either `MOVE_TO_ACTION`, `COPY_TO_ACTION`, `LINK_TO_ACTION` of C. If object C is an action, the args list does not include C. Also, the `action` is C.

The File Manager, along with its directory and folder objects, exemplifies how the desktop uses the move, copy, and link drop attributes. A user can drag and drop objects (files) to directory folders. File Manager defines `MOVE_TO_ACTION`, `COPY_TO_ACTION`, and `LINK_TO_ACTION` actions for folder objects. These actions perform the appropriate file system move, copy, and link system functions.

See `/usr/dt/appconfig/types/C/dtfile.dt` for an example of how to define the `MOVE_TO_ACTION`, `COPY_TO_ACTION`, and `LINK_TO_ACTION` attributes. See PG.dndPG.mkr.1, for information about how to use drag and drop.

## Example of Using the Data-Typing Database

This section contains example code of how to use data typing. You can find this example code in `/usr/dt/examples/dtdts/datatyping.c`. The example code displays the data type, icon name, and supported actions for each file passed to it. You can then use the `dtaction` client to run a supported action on the file. The usage for `datatyping` is:

    datatyping file1 [file2 ...]
    #include <Xm/Form.h>
    #include <Xm/Text.h>
    #include <Dt/Dts.h>

    #define ApplicationClass “DtDatatyping“

    static Widget text;

    static void DisplayTypeInfo(int, char**);

    int main(int argc, char **argv)
    {
        XtAppContext appContext;
        Widget toplevel, form;
        Arg args[20];
        int n;

        toplevel = XtAppInitialize(&appContext, ApplicationClass,

     NULL,  0,
            argc, argv, NULL, NULL, 0);

        if (argc == 1) {
            printf(“%s: No files specified.\n“, argv[0]);
            exit(1);
        }

        form = XmCreateForm(toplevel, “form“, NULL, 0);
        XtManageChild(form);
        n = 0;
        XtSetArg(args[n], XmNleftAttachment, XmATTACH_FORM); n++;
        XtSetArg(args[n], XmNrightAttachment, XmATTACH_FORM); n++;
        XtSetArg(args[n], XmNtopAttachment, XmATTACH_FORM); n++;
        XtSetArg(args[n], XmNbottomAttachment, XmATTACH_FORM); n++;
        XtSetArg(args[n], XmNeditable, False); n++;
        XtSetArg(args[n], XmNeditMode, XmMULTI_LINE_EDIT); n++;
        XtSetArg(args[n], XmNrows, 25); n++;
        XtSetArg(args[n], XmNcolumns, 90); n++;
        text = XmCreateScrolledText(form, “text“, args, n);
        XtManageChild(text);

        XtRealizeWidget(toplevel);
     if (DtAppInitialize(appContext, XtDisplay(toplevel), toplevel,

      argv[0],
                                                    ApplicationClass) == False) {
            printf(“%s: Couldn't initialize Dt\n“, argv[0]);
            exit(1);
        }

        DtDbLoad();

        DisplayTypeInfo(argc, argv);

        XtAppMainLoop(appContext);
    }

    static void DisplayTypeInfo(int argc, char **argv)
    {
        char *file;
        char *datatype;
        char *icon;
        char *actions;
        char str[100];
        int i;

        sprintf(str, “%-30s\t%-10s\t%-8s\t%-20s\n“,
                    “File“,
                    “DataType“,
                    “Icon“,
                    “Actions“);
        XmTextInsert(text, XmTextGetLastPosition(text), str);

        sprintf(str, “%-30s\t%-10s\t%-8s\t%-20s\n“,
                    “-------------------“,
                    “--------“,
                    “----“,
                    “-------“);
        XmTextInsert(text, XmTextGetLastPosition(text), str);

          for(i=1; i < argc; i++) {
            char *file = argv[i];

            /* find out the Dts data type */
            datatype = DtDtsFileToDataType(file);

            if(datatype) {
                /* find the icon attribute for the data type */
                icon = DtDtsDataTypeToAttributeValue(datatype,

       DtDTS_DA_ICON, file);
            }

      /*  Directly find the action attribute for a file */

            actions = DtDtsFileToAttributeValue(file,

       DtDTS_DA_ACTION_LIST);

            sprintf(str, “%-30s\t%-10s\t%-8s\t%s\n“,
                            file,
                            datatype?datatype:“unknown“,
                            icon?icon:“unknown“,
                            actions?actions:“unknown“);
            XmTextInsert(text, XmTextGetLastPosition(text), str);

            /* Free the space allocated by Dts */

            DtDtsFreeAttributeValue(icon);
            DtDtsFreeAttributeValue(actions);
            DtDtsFreeDataType(datatype);
        }