www.apache.org >jakarta.apache.org >jakarta.apache.org/poi


Navigation
Main

HPSF
Overview
How To
Internals
To Do

HPSF Internals: The Horrible Property Set Format
HPSF Internals: The Horrible Property Set Format

HPSF Internals

Introduction

A Microsoft Office document is internally organized like a filesystem with directory and files. Microsoft calls these files streams. A document can have properties attached to it, like author, title, number of words etc. These metadata are not stored in the main stream of, say, a Word document, but instead in a dedicated stream with a special format. Usually this stream's name is \005SummaryInformation, where \005 represents the character with a decimal value of 5.

A single piece of information in the stream is called a property, for example the document title. Each property has an integral ID (e.g. 2 for title), a type (telling that the title is a string of bytes) and a value (what this is should be obvious). A stream containing properties is called a property set stream.

This document describes the internal structure of a property set stream, i.e. the Horrible Property Set Format (HDF). It does not describe how a Microsoft Office document is organized internally and how to retrieve a stream from it. See the POIFS documentation for that kind of stuff.

The Horrible Property Set Format is not only used in the Summary Information stream in the top-level document of a Microsoft Office document. Often there is also a property set stream named \005DocumentSummaryInformation with additional properties. Embedded documents may have their own property set streams. You cannot tell by a stream's name whether it is a property set stream or not. Instead you have to open the stream and look at its bytes.


Data Types

Before delving into the details of the property set stream format we have to have a short look at data types. Integral values are stored in the so-called little endian format. In this format the bytes that make out an integral value are stored in the "wrong" order. For example, the decimal value 4660 is 0x1234 in the hexadecimal notation. If you think this should be represented by a byte 0x12 followed by another byte 0x34, you are right. This is called the big endian format. In the little endian format, however, this order is reversed and the low-value byte comes first: 0x3412.

The following table gives an overview about some important data types:

Name

Length

Example (Little Endian)

Example (Big Endian)

Bytes

1 byte

0x12

0x12

Word

2 bytes

0x1234

0x3412

DWord

4 bytes

0x12345678

0x78563412

ClassID

A sequence of one DWord, two Words and eight Bytes

16 bytes

0xE0859FF2F94F6810AB9108002B27B3D9 resp. E0859FF2-F94F-6810-AB-91-08-00-2B-27-B3-D9

0xF29F85E04FF91068AB9108002B27B3D9 resp. F29F85E0-4FF9-1068-AB-91-08-00-2B-27-B3-D9

The ClassID examples are given here in two different notations. The second notation without the "0x" at the beginning and with dashes inside shows the internal grouping into one DWord, two Words and eight Bytes.

Watch out: Microsoft documentation and tools show class IDs a little bit differently like F29F85E0-4FF9-1068-AB91-08002B27B3D9. However, that representation is (intentionally?) misleading with respect to endianess.


HPSF Overview

A property set stream consists of three main parts:

  1. The header and

  2. the section(s) containing the properties.


The Header

The first bytes in a property set stream is the header. It has a fixed length and looks like this:

Offset

Type

Contents

Remarks

0

Word

0xFFFE

If the first four bytes of a stream do not contain these values, the stream is not a property set stream.

2

Word

0x0000

4

DWord

Denotes the operating system and the OS version under which this stream was created. The operating system ID is in the DWord's higher word (after little endian decoding): 0x0000 for Win16, 0x0001 for Macintosh and 0x0002 for Win32 - that's all. The reader is most likely aware of the fact that there are some more operating systems. However, Microsoft does not seem to know.

8

ClassID

0x00000000000000000000000000000000

Most property set streams have this value but this is not required.

24

DWord

0x01000000 or greater

Section count. This field's value should be equal to 1 or greater. Microsoft claims that this is a "reserved" field, but it seems to tell how many sections (see below) are following in the stream. This would really make sense because otherwise you could not know where and how far you should read section data.


Section List

Following the header is the section list. This is an array of pairs each consisting of a section format ID and an offset. This array has as many pairs of ClassID and and DWord fields as the section count field in the header says. The Summary Information stream contains a single section, the Document Summary Information stream contains two.

Type

Contents

Remarks

ClassID

Section format ID

0xF29F85E04FF91068AB9108002B27B3D9 for the single section in the Summary Information stream.

0xD5CDD5022E9C101B939708002B2CF9AE for the first section in the Document Summary Information stream.

DWord

Offset

The number of bytes between the beginning of the stream and the beginning of the section within the stream.

ClassID

Section format ID

...

DWord

Offset

...

...

...

...


Section

A section is divided into three parts: the section header (with the section length and the number of properties in the section), the properties list (with type and offset of each property), and the properties themselves. Here are the details:

 

Type

Contents

Remarks

Section header

DWord

Length

The length of the section in bytes.

DWord

Property count

The number of properties in the section.

Properties list

DWord

Property ID

The property ID tells what the property means. For example, an ID of 0x0002 in the Summary Information stands for the document's title. See the Property IDs chapter below for more details.

DWord

Offset

The number of bytes between the beginning of the section and the property.

...

...

...

Properties

DWord

Property type ("variant")

This is the property's data type, e.g. an integer value, a byte string or a Unicode string. See the Property Types chapter for details!

Field length depends on the property type ("variant")

Property value

This field's length depends on the property's type. These are the bytes that make out the DWord, the byte string or some other data of fixed or variable length.

The property value's length is always stored in an area which is a multiple of 4 in length. If the property is shorter, e.g. a byte string of 13 bytes, the remaining bytes are padded with 0x00 bytes.

...

...

...


Property IDs

As seen above, a section holds a property list: an array with property IDs and offsets. The property ID gives each property a meaning. For example, in the Summary Information stream the property ID 2 says that this property is the document's title.

If you want to know a property ID's meaning, it is not sufficient to know the ID itself. You must also know the section format ID. For example, in the Document Summary Information stream the property ID 2 means not the document's title but its category. Due to Microsoft's infinite wisdom the section format ID is not part of the section. Thus if you have only a section without the stream it is in, you cannot make any sense of the properties because you do not know what they mean.

So each section format ID has its own name space of property IDs. Microsoft defined some "well-known" property IDs for the Summary Information and the Document Summary Information streams. You can extend them by your own additional IDs. This will be described below.

Property IDs in The Summary Information Stream

The Summary Information stream has a single section with a section format ID of 0xF29F85E04FF91068AB9108002B27B3D9. The following table defines the meaning of its property IDs. Each row associates a property ID with a name and an ID string. (The property type is just for informational purposes given here. As we have seen above, the type is always given along with the value.)

The property name is a readable string which could be displayed to the user. However, this string is useful only for users who understand English. The property name does not help with other languages.

The property ID string is about the same but looks more technically and is nothing a user should bother with. You could the ID string and map it to an appropriate display string in a particular language. Of course you could do that with the property ID as well and with less overhead, but people (including software developers) tend to be better in remembering symbolic constants than remembering numbers.

Property ID

Property Name

Property ID String

Property Type

2

Title

PID_TITLE

VT_LPSTR

3

Subject

PID_SUBJECT

VT_LPSTR

4

Author

PID_AUTHOR

VT_LPSTR

5

Keywords

PID_KEYWORDS

VT_LPSTR

6

Comments

PID_COMMENTS

VT_LPSTR

7

Template

PID_TEMPLATE

VT_LPSTR

8

Last Saved By

PID_LASTAUTHOR

VT_LPSTR

9

Revision Number

PID_REVNUMBER

VT_LPSTR

10

Total Editing Time

PID_EDITTIME

VT_FILETIME

11

Last Printed

PID_LASTPRINTED

VT_FILETIME

12

Create Time/Date

PID_CREATE_DTM

VT_FILETIME

13

Last Saved Time/Date

PID_LASTSAVE_DTM

VT_FILETIME

14

Number of Pages

PID_PAGECOUNT

VT_I4

15

Number of Words

PID_WORDCOUNT

VT_I4

16

Number of Characters

PID_CHARCOUNT

VT_I4

17

Thumbnail

PID_THUMBNAIL

VT_CF

18

Name of Creating Application

PID_APPNAME

VT_LPSTR

19

Security

PID_SECURITY

VT_I4


Property IDs in The Document Summary Information Stream

The Document Summary Information stream has two sections with a section format ID of 0xD5CDD5022E9C101B939708002B2CF9AE for the first one. The following table defines the meaning of the property IDs in the first section. See the preceeding section for interpreting the table.

Property ID

Property name

Property ID string

VT type

2

Category

PID_CATEGORY

VT_LPSTR

3

PresentationTarget

PID_PRESFORMAT

VT_LPSTR

4

Bytes

PID_BYTECOUNT

VT_I4

5

Lines

PID_LINECOUNT

VT_I4

6

Paragraphs

PID_PARCOUNT

VT_I4

7

Slides

PID_SLIDECOUNT

VT_I4

8

Notes

PID_NOTECOUNT

VT_I4

9

HiddenSlides

PID_HIDDENCOUNT

VT_I4

10

MMClips

PID_MMCLIPCOUNT

VT_I4

11

ScaleCrop

PID_SCALE

VT_BOOL

12

HeadingPairs

PID_HEADINGPAIR

VT_VARIANT | VT_VECTOR

13

TitlesofParts

PID_DOCPARTS

VT_LPSTR | VT_VECTOR

14

Manager

PID_MANAGER

VT_LPSTR

15

Company

PID_COMPANY

VT_LPSTR

16

LinksUpTo Date

PID_LINKSDIRTY

VT_BOOL



Property Types

A property consists of a DWord type field followed by the property value. The property type is an integer value and tells how the data byte following it are to be interpreted. In the Microsoft world it is also known as the variant.

The Usage column says where a variant type may occur. Not all of them are allowed in a property set but just those marked with a [P]. [V] - may appear in a VARIANT, [T] - may appear in a TYPEDESC, [P] - may appear in an OLE property set, [S] - may appear in a Safe Array.

Variant ID

Variant Type

Usage

Description

0

VT_EMPTY

[V] [P]

nothing

1

VT_NULL

[V] [P]

SQL style Null

2

VT_I2

[V] [T] [P] [S]

2 byte signed int

3

VT_I4

[V] [T] [P] [S]

4 byte signed int

4

VT_R4

[V] [T] [P] [S]

4 byte real

5

VT_R8

[V] [T] [P] [S]

8 byte real

6

VT_CY

[V] [T] [P] [S]

currency

7

VT_DATE

[V] [T] [P] [S]

date

8

VT_BSTR

[V] [T] [P] [S]

OLE Automation string

9

VT_DISPATCH

[V] [T] [P] [S]

IDispatch *

10

VT_ERROR

[V] [T] [S]

SCODE

11

VT_BOOL

[V] [T] [P] [S]

True=-1, False=0

12

VT_VARIANT

[V] [T] [P] [S]

VARIANT *

13

VT_UNKNOWN

[V] [T] [S]

IUnknown *

14

VT_DECIMAL

[V] [T] [S]

16 byte fixed point

16

VT_I1

[T]

signed char

17

VT_UI1

[V] [T] [P] [S]

unsigned char

18

VT_UI2

[T] [P]

unsigned short

19

VT_UI4

[T] [P]

unsigned short

20

VT_I8

[T] [P]

signed 64-bit int

21

VT_UI8

[T] [P]

unsigned 64-bit int

22

VT_INT

[T]

signed machine int

23

VT_UINT

[T]

unsigned machine int

24

VT_VOID

[T]

C style void

25

VT_HRESULT

[T]

Standard return type

26

VT_PTR

[T]

pointer type

27

VT_SAFEARRAY

[T]

(use VT_ARRAY in VARIANT)

28

VT_CARRAY

[T]

C style array

29

VT_USERDEFINED

[T]

user defined type

30

VT_LPSTR

[T] [P]

null terminated string

31

VT_LPWSTR

[T] [P]

wide null terminated string

64

VT_FILETIME

[P]

FILETIME

65

VT_BLOB

[P]

Length prefixed bytes

66

VT_STREAM

[P]

Name of the stream follows

67

VT_STORAGE

[P]

Name of the storage follows

68

VT_STREAMED_OBJECT

[P]

Stream contains an object

69

VT_STORED_OBJECT

[P]

Storage contains an object

70

VT_BLOB_OBJECT

[P]

Blob contains an object

71

VT_CF

[P]

Clipboard format

72

VT_CLSID

[P]

A Class ID

0x1000

VT_VECTOR

[P]

simple counted array

0x2000

VT_ARRAY

[V]

SAFEARRAY*

0x4000

VT_BYREF

[V]

void* for local use

0x8000

VT_RESERVED

0xFFFF

VT_ILLEGAL

0xFFF

VT_ILLEGALMASKED

0xFFF

VT_TYPEMASK


References

In order to assemble the HPSF description I used information publically available on the Internet only. The references given below have been very helpful. If you have any amendments or corrections, please let us know! Thank you!

  1. In Understanding OLE documents, Ken Kyler gives an introduction to OLE2 documents and especially to property sets. He names the property names, types, and IDs of the Summary Information and Document Summary Information stream.

  2. The ActiveX Programmer's Reference at http://www.dwam.net/docs/oleref/ seems a little outdated, but that's what I have found.

  3. An overview of the VT_ types is in Variant Type Definitions.

  4. What is a FILETIME? The answer can be found for example under http://www.vbapi.com/ref/f/filetime.html or http://www.cs.rpi.edu/courses/fall01/os/FILETIME.html. In short: The FILETIME structure holds a date and time associated with a file. The structure identifies a 64-bit integer specifying the number of 100-nanosecond intervals which have passed since January 1, 1601. This 64-bit value is split into the two dwords stored in the structure.

  5. This documentation origins from the HPSF description available at http://www.rainer-klute.de/~klute/Software/poibrowser/doc/HPSF-Description.html.





Copyright © 2002 Apache Software Foundation

Krysalis LogoCocoon Logo