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Internet of Things (IoT) software is notoriously complex, conventionally comprising multiple tiers. Traditionally an IoT developer must use multiple programming languages and ensure that the components interoperate correctly. A novel alternative is to use a single tierless language with a compiler that generates the code for each component and ensures their correct interoperation. We report a systematic comparative evaluation of two tierless language technologies for IoT stacks: one for resource-rich sensor nodes (Clean with iTask), and one for resource-constrained sensor nodes (Clean with iTask and mTask). The evaluation is based on four implementations of a typical smart campus application: two tierless and two Python-based tiered. (1) We show that tierless languages have the potential to significantly reduce the development effort for IoT systems, requiring 70% less code than the tiered implementations. Careful analysis attributes this code reduction to reduced interoperation (e.g. two embedded domain-specific languages (DSLs) and one paradigm versus seven languages and two paradigms), automatically generated distributed communication, and powerful IoT programming abstractions. (2) We show that tierless languages have the potential to significantly improve the reliability of IoT systems, describing how Clean iTask/mTask maintains type safety, provides higher order failure management, and simplifies maintainability. (3) We report the first comparison of a tierless IoT codebase for resource-rich sensor nodes with one for resource-constrained sensor nodes. The comparison shows that they have similar code size (within 7%), and functional structure. (4) We present the first comparison of two tierless IoT languages, one for resource-rich sensor nodes, and the other for resource-constrained sensor nodes.

Web applications are structured as multi-tier stacks of components. Each component may be written in a different language and interoperate using a variety of protocols. Such interoperation increases developer effort, can introduce security vulnerabilities, may reduce performance and require additional resources. A range of approaches have been explored to minimise web stack interoperation.This paper explores a pragmatic approach to reducing web stack interoperation, namely eliminating a tier/component. That is, we explore the implications of eliminating the Apache web server in a JAPyL web stack: Jupyter Notebook, Apache, Python, Linux, and replacing it with PHP libraries. We conduct a systematic study to investigate the implications for web stack performance, resource consumption, security, and programming effort.