You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: CityGML Application Domain Extension (ADE): overview of developments 
Chapter Title:  Disadvantages of ADE and open questions 
1. Abstract of Cited Paper (BIB001):  Abstract The Building Information Modeling (BIM) domain and the Geographic Information System (GIS) domain share a mutual need for information from each other. Information from GIS can facilitate BIM applications such as site selection and onsite material layout, while BIM models could help generate detailed models in GIS and achieve better utility management. The mapping between the key schemas in the BIM domain and the GIS domain is the most critical step towards interoperability between the two domains. In this study, Industry Foundation Classes (IFC) and City Geography Markup Language (CityGML) were chosen as the key schemas due to their wide applications in the BIM domain and the GIS domain, respectively. We used an instance-based method to generate the mapping rules between IFC and CityGML based on the inspection of entities representing the same component in the same model. It ensures accurate mapping between the two schemas. The transformation of coordinate systems and geometry are two major issues addressed in the instance-based method. Considering the difference in schema structure and information richness between the two schemas, a reference ontology called Semantic City Model was developed and an instance-based method was adopted. The Semantic City Model captures all the relevant information from BIM models and GIS models during the mapping process. Since CityGML is defined in five levels of detail (LoD), the harmonization among LoDs in CityGML was also developed in order to complete the mapping. The test results show that the developed framework can achieve automatic data mapping between IFC and CityGML in different LoDs. Furthermore, the developed Semantic City Model is extensible and can be the basis for other schema mappings between the BIM domain and the GIS domain. 
2. Abstract of Cited Paper (BIB002):  To be used as input in most simulation and modelling software, 3D city models should be geometrically and topologically valid, and semantically rich. We investigate in this paper what is the quality of currently available CityGML datasets, i.e. we validate the geometry/topology of the 3D primitives (Solid and MultiSurface), and we validate whether the semantics of the boundary surfaces of buildings is correct or not. We have analysed all the CityGML datasets we could find, both from portals of cities and on different websites, plus a few that were made available to us. We have thus validated 40M surfaces in 16M 3D primitives and 3.6M buildings found in 37 CityGML datasets originating from 9 countries, and produced by several companies with diverse software and acquisition techniques. The results indicate that CityGML datasets without errors are rare, and those that are nearly valid are mostly simple LOD1 models. We report on the most common errors we have found, and analyse them. One main observation is that many of these errors could be automatically fixed or prevented with simple modifications to the modelling software. Our principal aim is to highlight the most common errors so that these are not repeated in the future. We hope that our paper and the open-source software we have developed will help raise awareness for data quality among data providers and 3D GIS software producers. 
3. Abstract of Cited Paper (BIB003):  The validity of 3D primitives in 3D GIS datasets is often a prerequisite for using them in simulation and decision-making software, e.g. visibility analysis, noise pollution assessment, and energy estimation. However, while agreed definitions exist (in the international standard ISO19107), most software vendors ignore them and implement simpler 3D primitives, for instance by excluding interior boundaries in surfaces and/or solid. Such limitations prevent practitioners from exchanging and converting datasets, and thus to use these in other software and applications. I present in this paper val3dity, an open-source software to validate 3D primitives according to the international definitions of ISO19107. Practitioners can use it directly, without limitations: its code is freely available under the GPLv3 license, both binaries and a web-application are publicly available. It takes as input several formats (including the international standard CityGML), and outputs a report that helps users identify and understand the errors. I describe some of the engineering decisions supporting val3dity, and show that it can be used to validate real-world datasets.

Literature Review:
Because they solve the shortcomings of the default CityGML data model by enhancing it for certain purposes, ADEs entail an added layer of complexity in the data model BIB001 . Virtually always, developing an ADE by default means that it cannot be entirely interpreted by existing software, which is evident from the brief review of software (Section Overview of software support for ADE). A custom schema entails development of customised software solutions for modelling, exchange, visualisation, and utilisation of ADE-enabled CityGML datasets. It appears that it is uncommon to have the ADEs supported by software as authors often stop at the development of a schema BIB002 . Furthermore, ADEs rarely seem employed in other research. Their development usually ceases soon after publication, and in many cases work does not go beyond a research paper. While our review has shown that there is a relatively large number of ADEs, it is not common to find publicly available datasets that contain an ADE, and their validation has not been subject of research BIB003 BIB004 . Even though ADEs are intended to supplement CityGML, it is important to note that the geometries must be compatible with the Geography Markup Language (GML). This might be a disadvantage for purposes such as the conversion from IFC because it involves additional forms of geometry such as constructive solid geometry (CSG)  . The current ADE documentation leaves some open question, e.g. one of these relates to the level of detail: how would it be possible to denote the LOD of a spatial property introduced by an ADE? In CityGML, the LOD is only implicitly given by the name of the spatial property which starts with lodX (e.g. bldg:lod2MultiSurface). However, the CityGML specification does not elaborate how this should be achieved in an ADE. Therefore, when writing ADE-enabled software such as a viewer, it is not clear how it is possible to specify which ADE features are available in which LOD. Finally, it appears that, besides the CityGML standard, there is no authoritative publication focused on the ADE concept nor a '101 guide' (which we try to at least partially solve with this paper).