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Business Intelligence

Notes A metadata piece is a name/value pair that describes characteristics like author, name, and
rating. A route sign contains one or more metadata block titles. It can also identify a metadata
piece inside a metadata block. The following path expression comprises an App1 block which
comprises an IFD block which comprises the metadata piece:
/app1/ifd/{ushort=18249}
The Figure 4.3 illustrates the makeup of an example JPEG image with four origin metadata
blocks: App0, App1, XMP, and an unidentified block. Each emphasised item notes the type of
metadata (block or piece) and the query expression utilised to retrieve the data.

4.4.1 Anatomy of a Path Expression

To get access to metadata, a completely qualified query expression must be used in most cases.
So, what is a completely qualified query expression? A completely qualified expression is a
string that begins with the path feature slash (/), pursued by a navigation route to a metadata
block or a specific metadata piece. Each step within the navigation path is separated by a slash,
forming an expression for accessing a metadata block or a metadata item.

Example: The following is a completely trained query expression that accesses the
Microsoft photograph ranking in an IFD block that is nested in an App1 block:
/app1/ifd/{ushort=18249}
When this expression is parsed, it first explore for the App1 metadata block inside the image’s
metadata. If the App1 block is found, it continues it does seek looking for the nested IFD
metadata block. If the IFD block is discovered, it then examines for the specific metadata piece.

Notes If at any time a metadata block or piece is not found, it aborts the query.

4.4.2 Block Selection

The simplest metadata query expression is an expression to get a query reader/writer for an
exact metadata block. Getting a query reader/writer enables you to direct subsequent queries
exactly to a nested metadata block without considering with its parent block. A block selection
query expression is a navigation route to the yearned metadata block. For example, in the
preceding example there are five metadata blocks, two of which are nested in other metadata
blocks. The following are the path expressions to each metadata block in the JPEG example:
/app0
/app1
/app1/ifd
/app1/ifd/exif
/xmp
When you use a query reader/writer to execute a query, it comes back a new query reader/
writer that services queries inside the scope of the particular metadata block. For instance, if you
execute the query “/app1”, a new query book reader is got and queries to the new book reader
are relation to the App1 block. This means that the query “/ifd” is legitimate for the new reader
because the App1 block contains an IFD block. However, “/xmp” would not work because this
App1 block does not comprise an XMP metadata block.
For the JPEG example, the following indexed route expression can be utilised:
/[0]app1/[0]ifd

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