The terms self-sovereign identity (SSI) and decentralised identity are often used interchangeably, which results in increasing ambiguity when solutions are being investigated and compared. This article aims to provide a clear distinction between the two concepts in relation to the revised Regulation as Regards establishing the European Digital Identity Framework (eIDAS 2.0) by providing a systematisation of knowledge of technological developments that led up to implementation of eIDAS 2.0. Applying an inductive exploratory approach, relevant literature was selected iteratively in waves over a nine months time frame and covers literature between 2005 and 2024. The review found that the decentralised identity sector emerged adjacent to the OpenID Connect (OIDC) paradigm of Open Authentication, whereas SSI denotes the sector's shift towards blockchain-based solutions. In this study, it is shown that the interchangeable use of SSI and decentralised identity coincides with novel protocols over OIDC. While the first part of this paper distinguishes OIDC from decentralised identity, the second part addresses the incompatibility between OIDC under eIDAS 2.0 and Web3. The paper closes by suggesting further research for establishing a digital identity bridge for connecting applications on public-permissionless ledgers with data originating from eIDAS 2.0 and being presented using OIDC.

翻译：自我主权身份（SSI）与去中心化身份这两个术语常被混用，导致在研究和比较解决方案时产生日益严重的概念模糊性。本文旨在通过系统梳理eIDAS 2.0（《关于建立欧洲数字身份框架的修订条例》）实施前的技术发展脉络，清晰界定这两个概念在eIDAS 2.0语境下的区别。研究采用归纳探索法，在九个月时间内分多轮迭代筛选相关文献，涵盖2005年至2024年的学术成果。文献综述表明，去中心化身份领域脱胎于开放认证的OpenID Connect（OIDC）范式，而SSI则标志着该领域向基于区块链解决方案的转型。本研究发现，SSI与去中心化身份的混用现象恰与OIDC基础上衍生的新型协议同期出现。论文第一部分辨析OIDC与去中心化身份的本质差异，第二部分则探讨eIDAS 2.0框架下的OIDC与Web3之间的兼容性问题。最后提出未来研究方向：构建数字身份桥梁，以连接基于公开无许可账本的应用与源自eIDAS 2.0并通过OIDC呈现的数据。