Page 54 - DCAP606_BUSINESS_INTELLIGENCE

Unit 4: Understanding OLAP

In the query language, all indexes start at zero. In the previous expression, the first zero queries Notes
for the first App1 block and the second zero queries the first nested IFD block. Index notation can
still be utilised even when multiple blocks of the identical kind do not live. If the example JPEG
includes a second App1 block with an embedded IFD block, the expression “/[1]app1/ifd” would
be utilised to access the second App1 block.

The following expression accesses the Microsoft Photo ranking in the XMP block:
/xmp/xmp: Rating
The “xmp:” part of the expression is a schema identifier. XMP is an extensible benchmark and
allows third party entities to publish their own schemas which indicate how to shop certain
metadata items.

The following data types are accepted by the query dialect:
char
uchar
short
ushort
long
ulong
int
uint
longlong
ride high
twice
str
wstr
guid
bool
The query dialect is not case sensitive and treats all individual features as lowercase. However,
some metadata formats (such as XMP) are case sensitive. When employed with a case-sensitive
metadata format, use the backslash (\) feature when you want to identify an uppercase feature.
The following table supplies some example expressions and descriptions of their interpretations
by the query dialect parser.
Table 4.1: Examples of Expression and Descriptions
Expression Description
ifd/xmp/exif:Author Corresponds to the following navigation path: IFD block -> XMP
block -> "Author" property in the "Exif" schema.
/[1]ifd/[0]xmp/exif:Author Same as the first item in this table except that the [#] prefix describes
which item to navigate in event of a name collision.
/ifd/{ushort=700}/Author Same as the first item in this table except that it uses a data
expression to reference the XMP block instead of the block name
"xmp" (XMP block is embedded under the unsigned short tag
identifier 700). Also, the "Author" property does not specify a
schema. The query parser will try to match the property across all
schemas and return the first match.
/ifd/xmp Provides a navigation path to a metadata block. If the block is found,
a new metadata reader/writer is returned.
/[*]tEXt/Keyword Gets or sets the Keyword property for a PNG chunk. Because the
PNG metadata specification allows for multiple chunks of a
particular type, the [*] notation gets/sets the data PNG chunk with
the appropriate property. Per the PNG specification, no two chunks
can have the same properties.

Source: http://msdn.microsoft.com/en-us/library/windows/desktop/ee719796(v=vs.85).aspx

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