Software as a service (SaaS) is a model of providing remotely hosted service, (usually through a paid subscription) software. Known Saas examples are Google Apps, Web Apps or LotusLive (IBM) Office.
Data as a Service is the provision of outsourced somewhere on the network. The data is mainly consumed by mashups. Platform as a Service. This type of cloud computing can make available to companies or individuals a runtime environment, letting them control the applications they can install, configure and use themselves. It allows you to host applications that are not suited to the SaaS model (specific applications, applications under development).
Infrastructure as a service is a model where the company has a paid subscription to IT infrastructure (servers, storage, network) which is physically located at the supplier. This representation of the different service models shows how responsibilities are theoretically distributed according to internal models, IaaS, PaaS, SaaS. In addition to these service models, there is a multitude of service models mechanically built on the phrase as a service.
BPaaS: this is the concept of Business Process as a Service (BpaaS), which involves outsourcing a business process sufficiently industrialized to go directly to the managers of an organization, without requiring professional help of IT.
Desktop as a Service: The Desktop as a Service (DaaS) is outsourcing a Virtual Desktop Infrastructure with a service provider. Generally, Desktop as a Service is offered with a paid subscription.
Network as a Service (NaaS): The Network as a Service is the provision of network services by Cloud Technology Companies following the concept of Software Defined Networking (SDN). Staas: Storage as a Service is the file storage with external service providers that host them on behalf of their clients. General public services such as SugarSync and Box.net, offer this type of storage, most often for backup or file sharing. Other examples: Amazon Simple Storage Service, Dropbox, Google Drive, iCloud, SkyDrive, Ubuntu One, Windows Live Mesh.
Unlike individuals who have very little room to maneuver, companies are forced to sign contracts the cloud services they buy. Contract terms of Cloud Technology Companies mainly cover the availability, security, confidentiality and support. The guarantees of confidentiality, traceability of operations and quality of services are clearly defined especially for critical applications or handling of personal data, strategic or bound by any applicable law.
Note that in terms of regulatory compliance, it is the client company that is legally responsible, the supplier acting as a subcontractor. The reversibility must be controlled precisely in the contract between all stakeholders. Also, watch for:commitments availability, frequency of backups and the respective roles of the different actors, the number ranges from one to four).