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in the previous step to the set of available data stores and data services that
have been categorized according to the same nonfunctional and functional
properties. Implementing this step requires data stores and data services to
be previously specified according to the set of functional and nonfunctional
properties either directly by the cloud providers or by the users of the meth-
odology. The management and configuration capabilities required for this
specification, however, can be used at a later time to also make new cloud
data stores and data services available (FR
4
).
5.4.2.4 Step 4: Describe Source Data Store or Data Service
As it is not sufficient to consider only where the data has to be migrated, in
step 4 the
functional and nonfunctional properties of the source data store or data
service
are also described to identify and solve potential migration conflicts,
such as the database technology used or whether the location is on or off the
premises (FR
5
).
5.4.2.5 Step 5: Identify Patterns to Solve Potential Migration Conflicts
The use of cloud technology leads to challenges such as incompatibilities
with the database layer previously used or the accidental disclosing of criti-
cal data (e.g., by moving them to the public cloud). Incompatibilities in the
database layer may refer to inconsistencies between the functionalities of an
existing traditional database layer and the characteristics of an equivalent
cloud data hosting solution. Therefore, in the fifth step conflicts are identi-
fied by checking the compatibility of the properties of the target data store
selected in step 3 with the properties of the source data store or service used
before the migration (FR
5
). As a way to address these conflicts, in previous
work (Strauch et al., 2013c) we have defined a set of
cloud data patterns
as the
best practices to deal with them that can be reused here.
5.4.2.6 Step 6: Refactor Application Architecture
As the migration of the database layer also has an impact on the remaining
application layers (presentation and business logic; Fowler et al., 2002), the
methodology should provide guidelines and hints on what should be con-
sidered for the refactoring of the application. Special focus should be given
to the adaptation of the network, the data access layer, and the business logic
layer of the application, depending on the outcomes of the previous steps
(FR
7
). Networking adaptation might require, for example, the reconfigura-
tion of open ports in the enterprise firewall. Although the cloud data store
might be fully compatible with the data store previously used, the migration
requires at least a change to the database connection string in the data access
layer. The impact of the database layer migration to the cloud on the business
logic layer depends on several aspects, such as the migration scenario and
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