From Conventional to Multiversion Data Warehouse - Evolving Application Domains of Data Warehousing and Mining - page 53

Instance sharing approaches are also known
as data sharing approaches. According to this ap-
proach (Wrembel, 2005a), a record is physically
stored in a data warehouse only once and shared by
one or more versions. The data common between
versions is stored in parent version and shared by
child versions. In case of changes, a new record of
only the changed data is stored physically in the
new version. Relationship between schema and
instance version is given in Figure 8.
Sharing of a record stored by the parent version
is done by attaching a bitmap with each record and
for each version. So, one bitmap gives the informa-
tion whether a particular record is attached with
the version or not. If the value of the bit is 0 the
record is not shared with the version, whereas if
the value of the bit is 1 it is shared with the version.
Let A1, A2 ….An be the attributes of the table in
parent version (V0.0) with data values Di1,Di2,
… where I is the row id. Let V1.0 … Vw.x, Vq.r,
Vy.z be the child versions of the data warehouse.
The parent version shares data with all versions
with an exception of Vq.r. Generally, the bitmap
will look like shown in Table 1.
In case versions of the data warehouse are
maintained in such a way that each version has

its own data physically stored, the size of the data
warehouse will become much larger. By using
the data sharing approach, the size of the data
warehouse will be greatly reduced. However, at
the same time query performance will be impacted
as well. Therefore a balance between query per-
formance and size of the data warehouse should
be maintained.

MetAdAtA In MultIverSIon dW

In order to support the data warehouse lifecycle
managing relationships between versions for data
sharing and for retrieval from multiversion data
warehouse, multifaceted data is required to be

Table 1. Data sharing scheme between versions
of data warehouse

A1 A2 … An V1.0 … Vw.x Vy.z

D11 D12 D1n 1 1 1

D21 D22 … D2n 1 1 1

… … … …

Dp1 Dp2 … Dpn 1 1 1

Figure 8. Relationship among schema and instance versions (adopted from Bebel, 2006)