## 7 Discussion of Quality Properties  
Provided in the literature are many quality properties to measure the Quality of Service in the IoT [48]; we focus on availability and reliability as two broad but vital concepts for commenting on the quality of a provided service. The emerging challenge from this discussion is to characterize the provided services in terms of how they serve the user's requirements under different conditions in the physical environment. This increases user engagement by contributing to the creation of a flexible user-centric architecture. Additionally, it is essential to comment on the aforementioned quality properties and set future directions for creating a QoS framework for the IoT. At the same time, this specific discussion validates the reason for the existence of the proposed architecture and the CEP model, significantly strengthening its guarantees for the adoption of these practices in a production environment.  
According to [49; 50], there are many quality properties, including accessibility, availability, elasticity, installability, interoperability, maintainability, privacy, reliability, resource utilization, responsiveness, scalability, security, testability, and usability. In this paper, we focus on two basic quality properties that can provide fundamental validation of the quality of a provided service based on the overall behavior of the system. These quality properties are Availability and Reliability [49; 50]. Studying the quality properties and analyzing trade-offs helps users make decisions to flexibly and effectively manage IoT Physical under different circumstances and situations. Moreover, these particular quality properties correspond with the extent to which user needs are satisfied when the system is used in a particular operation and the extent to which the system can adapt to new operational conditions. Formally, this is the extent to which the system provides functions that meet stated and implied needs when used under specified conditions (bottom-up).  
In this paper, a significant challenge emerges related to the quality properties each Composite Transformation may or may not serve. Each Composite Transformation serves specific quality properties that fit different use cases based on the requirements of the user and the conditions of the physical world. Likewise, each scenario serves specific quality properties to a different degree and is based on certain conditions, which are known and generally maintained for each execution of the scenario without it being binding, since an IoT ecosystem is naturally complex and often unpredictable.  
When we study an IoT system, many factors [48; 49; 50; 51] influence certain metrics, whether qualitative or quantitative. Moreover, these factors usually concern all layers of a typical IoT architecture [6; 52]. However, in the example and scenarios we present in Section 6, we focus on two basic non-ideal conditions regarding IoT Physical. More specifically, the errors we study are (i) sensor failure that includes physical damage, disconnection, or any other reason that may set the sensor unavailable and (ii) indefinite delay of data transmission from a functional and available sensor. Our choice is made to preserve the simplicity of the example but also to record and highlight how we deal with the increasing complexity that basic real-world situations may introduce. Next, we discuss the quality properties per scenarios we have already presented.