You can design a Job with consecutive tMatchGroup components
to create data partitions based on different blocking keys.

For example, you want to find duplicates having either the same city or the same zip code
in a customer database. In this particular case, you can use two consecutive
tMatchGroup to process the data partitions:

• One tMatchGroup in which the column “city” is defined as a
  blocking key.

• One tMatchGroup in which the column “ZipCode” as a
  blocking key.

What is multi-pass matching?

The idea behind multi-pass matching is to reuse the master records defined in the
previous pass as the input of the current tMatchGroup
component. Multi-pass matching is more effective if the blocking keys are almost not
correlated. For example, it is not relevant to define the column “country” as a
blocking key and the column “city” as another blocking key because all the
comparisons made with the blocking key “city” will also be done with blocking key
“country”.

When using multi-pass matching with the VSR algorithm, only master records of size 1
– records that did not match any record – are compared with master records of any
size. There are no comparisons between two master records that are derived from at
least two children each.

An example of multi-pass matching

In the following example, the dataset contains four records. It is assumed that the
first tMatchGroup component has a blocking key on the column
“ZipCode”, and the second tMatchGroup component has a
blocking key on the column “city”. The attribute “name” is used as a matching
key.

After the first pass, records 1 and 3 are grouped, and records 2 and 4 are grouped.
In these groups, record 1 and record 2 are master records.

In the second tMatchGroup, only the master records from the
first pass, record 1 and record 2, are compared. Since their group size is strictly
greater than 1, they are not compared.

The following results are returned:

When running the T-Swoosh algorithm with the same parameters and the Most
common survivorship function, the following results are
returned: