XMP Specification Part 3: Storage in Files - Adobe

2.4.2 INDD, INDT (Adobe InDesign®)
InDesign document files (.indd) and InDesign template files (.indt) are primarily paged database files. They
have 4 KB pages with a leading pair of master pages to allow single write commits. The detailed structure of the
database is proprietary.
Externally editable XMP is supported for database files from InDesign 2.0 and later through a "contiguous
object" section at the end of the file. It is possible to modify, even extend, the XMP in the contiguous object
section. It is not possible to add XMP to a database that has none without intimate knowledge of the database.
In brief, the active master page tells how many database pages the file contains. The contiguous object section
begins after the last database page and extends to the end of the file. It contains copies of database objects,
stored in a contiguous (nonpaged) manner.
Figure 5 shows the layout. In the figure:
• The curved arrow represents the fact that the current (active) master page indicates how many database
pages there are, enabling an application to find the beginning of the contiguous object section.
• Main pages: This is the main part of the database file, comprised of 4 KB pages. The first two pages--the
master pages--are used to determine how big this part of the file is (that is, where the contiguous object
copies start). Otherwise, this data can be ignored when scanning for XMP data, and you should never alter
this portion of the file if you are modifying XMP data.
• Contiguous objects: Following the data pages, copies of contiguous objects are written, and each has a
special header and trailer. Here you would find any XMP objects, and you may rewrite this part of the file if
you need to expand the file’s XMP data beyond whatever padding is supplied in the XMP packet.
• Zero padding: The file is zero padded so that the file size is a multiple of 4 KB.
Figure 5 — InDesign file layout
The majority of an InDesign database file consists of the 4 KB pages that comprise the transacted database
storage. You can use the first two pages in the file, called the Master Pages, to determine whether contiguous
objects are present, where they are, and whether they include any XMP metadata objects that contain XMP
packets. InDesign document databases do typically contain XMP metadata, but this is not strictly required.
Other types of InDesign files, such as book files, do not currently contain metadata.
• For details of the Master Page structure, see 2.4.2.3, “Master page structure”.
• For details of the Header and Trailer that enclose each contiguous object, see 2.4.2.4, “Header and trailer
structure”
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