What is the Dialog Tag Language?

In Why the Dialog Tag Language (DTL)? we referred to DTL as a tag-based markup language that is similar to IBM® BookMaster®. The two have much in common. For example, markup is a term that is usually associated with documentation. It is an old typesetting term that formerly meant the instructions with which a document was "marked up" to show how the document should be set in type.

Today, this definition has been expanded to include information that is added to a document to enable a person or system to process it. Just as markup information can describe a document's characteristics or the processing to be performed, it can also describe the characteristics or processing related to dialog elements. This is where the tags come in.

We call DTL a tag-based markup language simply because the markup consists of tags that determine not only what each element is, but also how it is processed. To convert the dialog elements into a format that is usable by ISPF, you must convert them to ISPF elements with ISPDTLC, the ISPF conversion utility. (See What is the ISPF conversion utility? for more information.)

Another thing that DTL and BookMaster have in common, of course, is the tags themselves, which have these similarities:

They are very short and easy to remember.
They are often accompanied by text.
Many DTL tags are almost identical to corresponding BookMaster tags.

These are all reasons that familiarity with BookMaster makes it easy to learn DTL. For example, we could have created the preceding bulleted, or unordered list in BookMaster by editing a file using an editor and typing this:

:ul compact.
  :li.They are very short and easy to remember.
  :li.They are often accompanied by text.
  :li.Many DTL tags are almost identical to corresponding BookMaster tags.
:eul.

You could create a similar list for an information panel by using DTL tags with the same text:

<ul compact>
  <li>They are very short and easy to remember.
  <li>They are often accompanied by text.
  <li>Many DTL tags are almost identical to corresponding BookMaster tags.
</ul>

Here, the <ul> and </ul> tags, respectively, begin and end the unordered list. This type of list is called an unordered list because the list items are not numbered. The individual list items are defined by the <li> tags and consist of the accompanying text.

As you can see from the preceding example, DTL tags act as control words that specify how the text of source files is interpreted by the conversion utility. This concept is based on the Standard Generalized Markup Language (SGML), which is a standard of the International Standards Organization (ISO). The conventions of the Dialog Tag Language are based on the SGML standard.

After you are finished marking up a source file, use the conversion utility to convert the file into a format usable by your ISPF application. In addition to processing the file, the conversion utility also checks and verifies the syntax of your markup, and notifies you of any errors. After conversion, the elements you defined in your source file are stored within ISPF libraries.

You can use ISPF dialog test facilities to display application panels and messages after they have been converted. Displaying your panels is a good idea to make sure they format properly.

You should now have a basic understanding of DTL and how it works. The next section builds on this understanding by describing the types of elements that you can define with DTL.