Cloud computing is a business paradigm that changes the way to evaluate information systems and computing resources. Cloud requirements can rapidly change and new service capabilities are often requested in order to adapt to new business scenarios. The existing works are generally focused in a limited number of requirements and capabilities. The aim of this project is to understand the multifaceted components of a service and to give guidelines towards requirements engineering for cloud computing. Thus, cloud services are analyzed by different aspects called dimensions and five dimensions are proposed (i.e., Contractual, Financial, Compliance, Operation, and Technical). Cloud dimensions are graphically presented in conceptual and semantic models (RE4Cloud Semantic Model: OWL file), because each dimension has specific entities, properties, and relationships. Different specialists and experts may be requested to evaluate particular dimensions during cloud service adoption, and this approach can guide those activities, support requirements specification, and guide system analysis for cloud computing.

Cloud Dimensions in RE4CLOUD Semantic Model

This research started exploring characteristics of cloud services using three types of sources: scientific source (i.e. journals, conferences, and books), organization source (i.e. standard-based organizations such as ISO, ENISA, and NIST), and practitioners source (i.e. SLAs and forums). Five Cloud Dimensions were already identified by grouping related concepts and characteristics from the sources, which can be considered as an extension of cloud computing definition.

Cloud dimensions are indentified and classified as: (a) Contractual Dimension: it represents all the information about the contract, service agreements, and stakeholders; (b) Financial Dimension: it involves economic and finance aspects of cloud services, such as billing data, payment and pricing; (c) Compliance Dimension: it refers to all rules and norms that cloud services should compliance with, such as standards, certifications, and security; (d) Operation Dimension: It is about service maintainability, resources management and access control; and (c) Technical Dimension: it involves parameters of metering services, such as values, functions, constraints, metrics, and units.

Each dimension covers a specific aspect of cloud contracts and services, and SLA negotiation may require the participation of specialists and experts for analyzing it (e.g. finance and accounts advisors for Financial Dimension, lawyers and legal counselors for Contractual Dimension). Being focused on cloud dimensions simplifies requirements elicitation and SLA negotiation, and requirements changes can be more controlled and predictive in cloud business processes. The cloud dimensions were transformed to a semantic model and the ontology RE4CLOUD (Requirements Engineering for Cloud Computing) was created.

Evaluation of RE4CLOUD using SPARQL

The ontology RE4CLOUD is formalized in OWL (Web Ontology Language), so it is compatible with data models constructed in RDF (Resource Description Framework) and it can be mapped within RDF graphs, and vice versa.

RDF specifies knowledge in the form of triplets and the query language SPARQL (Simple Protocol and RDF Query Language) is in charge of consulting and manipulating these triplets, coming from different data sources.

During the construction of RE4CLOUD, some competency questions were created to justify the existence of classes and properties in the proposed ontology. These questions were formalized in SPARQL.

The competency questions were answered in an evaluation version of Top Braid Composer ^TM Standard Edition (TBC-SE). TBC-SE is a modeling tool compatible with the RDF, OWL and SPARQL languages, and it is used to develop ontology models, data set integration and applications for the Semantic Web.

Question 1: The results are all classes and relationships related to the Service Level Agreement.

Question 2: The results are attributes related to Service Contract, such as Effective Data, Running Time and Data Deletion Date. Those data properties are very significant, because they show the temporal event in a contract.

Question 3: The results are Pricing Models for cloud services. The Pricing Models are: Pay Per Unit, Pay Per Use, Prepaid, Subscription and Tiered Usage.

Question 4: The results are classes, properties and relationships, related to Compliance Dimension of Service Level Agreements.

Question 5: The results are all classes related to virtual and physical resources in Service Management.

Question 6: The results are all data properties (attributes) and object properties (relationship) used to define Metrics of Cloud Computing.