Guest Editors' Introduction

C loud computing has become a scalableservices consumption and delivery platform in the field of services computing.1 It aims to share resources among cloud-service consumers and cloud partners and vendors in the value chain shown in Figure 1. The resource sharing at different levels results in various cloud offerings: infrastructure as a service (IaaS) focuses on hardware and IT infrastructure management, platform as a service (PaaS) concentrates on middleware and design tools as a service, software as a service (SaaS) deals with traditional software applications such as customer relationship management or social networking as a service, and business process as a service (also known as the business cloud) offers value-added services. To tie some of these aspects together, we use the cloud computing open architecture (CCOA)2 as the landscape to illustrate some hot topics about cloud computing.