# Metaverse Architectures: A Comprehensive Systematic Review of Definitions and Frameworks
## 4 Discussion
### Metaverse Architecture
#### 4.2.1 Hierarchical Structure of the Metaverse Architectures  
The study investigates general-purpose metaverse architectures employing models with layered, modular, and ordered frameworks. These designs help to enable the methodical conceptualisation of the metaverse and ease the comparison of fundamental structural elements. The analysis considered three sample models: the three-layer framework by [PERSON] et al. [48], the five-layer architecture introduced by [PERSON] et al. [5], and the four-layer structure jointly presented by [PERSON] et al. [78] and [PERSON] et al. [31]. The selection of these models was based on their established recognition within the academic literature as general-purpose metaverse architectures, their conceptual clarity, and structural integrity. Their recurrent presence in comparative studies and their fundamental impact on the development of metaverse design principles additionally substantiate their incorporation. To ensure a systematic and meaningful comparison across these hierarchical frameworks, this analysis uses several comparison criteria. These criteria include (1) functional domain coverage, (2) granularity of layer differentiation, and (3) support for modularity, scalability, and interoperability. The three metaverse architectural models each employ a hierarchical structure to incrementally refine the division of system responsibilities, which enables conceptual clarity and architectural adaptability across diverse implementation scenarios. Figures 3-5 show representations of three-layer, four-layer and five-layer metaverse architecture, respectively, arranged from top to bottom layer. Each of these figures will be discussed separately. 1. Three-Layer Architecture: The three-layer architecture is the basic structure. Figure 3 illustrates that the three-layer metaverse architecture is structured into three principal components: infrastructure, interactivity, and ecosystem, emphasising essential functionality. * Ecosystem Layer: It supports the seamless operation of the entire Metaverse, creating a parallel, dynamic, and interactive virtual world. * Interactivity Layer: This layer serves as an interface between the virtual and real worlds, allowing the real world to be connected to the metaverse and the metaverse to be realised. * Infrastructure Layer: The infrastructure layer contains the fundamental requirements for supporting the operation of a virtual world, including computation, communication, blockchain and storage. Blockchain is often incorporated at a fundamental level to guarantee decentralisation, transparency, and security within virtual environments. In this architecture, blockchain not only ensures distributed data integrity but also facilitates smart contracts and tokenised interactions that support higher-level functions, such as digital economies and decentralised governance. Although its structural role is within the infrastructure, its influence extends across layers, particularly within the ecosystem layer, highlighting the merging of technical and socio-economic design in metaverse systems. * Four-Layer Architecture: The four-layer metaverse architecture offers a disciplined framework that differentiates important elements engaged in the interaction between the real and virtual worlds. As illustrated in Figure 4, this architecture is composed of the following layers:
* Physical World: The physical layer includes key stakeholders, which are users, IoT and sensor networks, virtual services providers and physical space providers. Figure 4: The four-layer metaverse architecture, introducing the metaverse engine and distinguishing between the physical and virtual worlds. Figure 3: The three-layer metaverse architecture. Virtual World: The virtual world layer contains a virtual environment designed for education, trading, goods and services. Users are represented as digital avatars, allowing them to engage in activities that closely resemble those in the real world. 2.