# What Is an Open IoT Platform?
## 1 Introduction and Motivation  
After decades of development, the Internet of Things (IoT) has evolved into a fully fledged ecosystem including hardware, software, physical objects and people with complex interactions and data exchanges. The number of users, services and applications with IoT is rapidly growing in many different domains [1]. The development of new intelligent applications can benefit from IoT in almost every field from personal everyday life to environment and society. [PERSON] [2] classifies the various IoT applications into three major domains--industrial domain, smart city domain and health well-being domain--and gives many related applications as examples such as farm management [3], smart grid [4], and remote healthcare [5]. Because of the huge potentialities in IoT, the demands for new services and applications are massive. The IoT market is predicted to grow, by some estimates, from 50 billion [6] to 100 billion [7] devices by 2020. Other more modest projections state that there will be 24 billion [1] and 26 billion [8] devices by the same year. The large number of devices builds a solid foundation as the devicelayer. Numerous services and applications can be further developed based on devices with many different technologies [9]. However, such a scale of devices and various enabling technologies make the development of IoT systems complicated and difficult. For these issues, IoT platforms play a significant role in helping the integration and development of IoT systems. As a result, new IoT platforms are constantly emerging, which forms a new layer in Cyber-Physical Systems (CPSs) [10]. These IoT platforms already offer heterogeneous ways to access them and their data [11]. According to the [PERSON] et al. [12] an \"IoT platform is defined as the middleware and the infrastructure that enables the end users to interact with smart objects\". There are different types of platforms available that often are referred to as IoT platforms, such as device-to-device, cloud-based and device-to-cloud platforms (which are often also referred to as enterprise platforms that face a vendor lockdown [13; 14; 15]). The diversity of IoT platforms and their complex offerings creates confusion among developers and researchers, as well as end users. As such, today the IoT is mainly associated with vertically integrated systems that often are closed and fragmented in their applicability. For example, there are multiple IoT platforms, which partially comply with standards; diverse mobile platforms and systems, where the operating systems and programming languages are different; and physical devices that have varying characteristics [11; 16]. With such closed nature and fragmentation in the market, developers usually struggle to reach critical mass, and even end users need to navigate through different brands and understand which devices are compatible in relation to which IoT platforms. Commercial or proprietary IoT platforms carry a pricing model and often promote vendor lock-in. Thus, often IoT platform providers lack support of new protocols, tools and data formats in time due to a constantly changing IoT landscape. Openness, on the other hand, is one of the emerging trends that is evident in IoT domains [16; 17; 18]. More and more IoT players are motivated to use open systems due to the associated benefits such as convenience and fast development resulting in major cost savings for the industry [17; 19]. From a general perspective, innovation, entrepreneurship, creativity and new business models also require openness to build a valuable ecosystem based on our previous experience in the Internet economy [20]. Several interesting studies provide analysis of some open and closed IoT platforms [12; 21; 22; 23; 24]. A study on gap analysis of IoT platforms lists a representative sample of both open and closed ones, providing an overview of actual platforms, their heterogeneity, type, deployment architectures, availability and data access [12].