Informatica Tutorials

Big Data Analytics

Physical Extraction Methods

Depending on the chosen logical extraction method and the capabilities and
restrictions on the source side, the extracted data can be physically extracted by two
mechanisms. The data can either be extracted online from the source system or from
an offline structure. Such an offline structure might already exist or it might be
generated by an extraction routine.

There are the following methods of physical extraction:
■ Online Extraction
■ Offline Extraction

Online Extraction
The data is extracted directly from the source system itself. The extraction process can connect directly to the source system to access the source tables themselves or to an intermediate system that stores the data in a preconfigured manner (for example, snapshot logs or change tables). Note that the intermediate system is not necessarily physically different from the source system.

With online extractions, you need to consider whether the distributed transactions are using original source objects or prepared source objects.

Offline Extraction
The data is not extracted directly from the source system but is staged explicitly
outside the original source system. The data already has an existing structure (for
example, redo logs, archive logs or transportable tablespaces) or was created by an
extraction routine.

You should consider the following structures:
■ Flat files
Data in a defined, generic format. Additional information about the source object
is necessary for further processing.
■ Dump files
Oracle-specific format. Information about the containing objects may or may not
be included, depending on the chosen utility.
■ Redo and archive logs
Information is in a special, additional dump file.
■ Transportable tablespaces
A powerful way to extract and move large volumes of data between Oracle

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