目录
1. 是什么？
2. 功能特性？
3. 核心概念？
3.1. Virtual Knowledge Graph (VKG)
3.2. RDF
3.3. SPARQL query
3.4. Mappings
3.5. Ontology
3.6. VKG specification
3.7. SPARQL endpoint
4. 总体流程1. 是什么？
Ontop is a Virtual Knowledge Graph system. It exposes the content of arbitrary relational databases as knowledge graphs. These graphs are virtual, which means that data remains in the data sources instead of being moved to another database.（概要：Ontop 是虚拟只是图谱系统，它能把关系型库中的数据映射成知识图谱）
Ontop translates SPARQL queries (opens new window)expressed over the knowledge graphs into SQL queries executed by the relational data sources. It relies on R2RML mappings (opens new window)and can take advantage of lightweight ontologies. （概要：Ontop 能把基于 RDF 的 SPARQL 查询转换为基于关系型数据库的 SQL 查询。它底层依赖的是 R2RML 映射模式。）
2. 功能特性？
3. 核心概念？
3.1. Virtual Knowledge Graph (VKG)
A Knowledge Graph (KG) is, in our terminology, a graph using the RDF data model.（概要：知识图谱是使用 RDF 数据模型的图）
A Virtual KG (VKG) is a virtual representation in RDF of non-RDF data, which is generally relational data. With a VKG, the data remains in the data sources in its original format but can be virtually represented as an RDF graph.（概要：虚拟知识图谱是非 RDF 数据（例如：关系数据）的一种虚拟表达（映射））
3.2. RDF
The Resource Description Framework (RDF) is one of the two main data models for graphs (together with property graphs). RDF mainly targets data integration applications while property graphs are used for building graph databases. （概要：RDF、属性图是两种主要的图数据模型，RDF 主要用于与应用进行集成，而属性图主要用来构建图数据库）
In RDF, data is modelled using classes and properties.
3.3. SPARQL query
SPARQL is the standard query language for RDF graphs. （概要：SPARQL 是 RDF 图的标准查询语言）
Ontop is capable of answering SPARQL queries expressed over the VKG. Ontop translates these SPARQL queries into SQL queries, which are then executed over the relational data sources.（概要：Ontop 能把作用于 RDF（虚拟知识图谱）上的 SPARQL 查询，转换为作用域关系数据库的 SQL 查询）
3.4. Mappings
Mappings specify the correspondence between the data models of the relational data sources and the RDF graph. Ontop supports the R2RML standard mapping language and the Ontop mapping language, which is fully interoperable with R2RML. （概要：映射是关系型数据库与RDF图之间的对应关系。）
3.5. Ontology
An ontology specifies the formal relations between the classes and properties used by the RDF graph. It is mainly used for enriching the RDF graph by, for instance, taking account of class hierarchies. （概要：Ontology（本体）是用于构建 RDF 图的正式描述（类、属性、关系））
3.6. VKG specification
VKG specifications are composed of mappings and optionally of ontologies.
3.7. SPARQL endpoint
A SPARQL endpoint is a standardized HTTP-based Web API. It makes the RDF graph queryable by any HTTP client. （概要：SPARQL 终端是能对外提供基于HTTP 协议的 SPARQL 查询的服务）
Ontop enables VKG specifications to be deployed as SPARQL endpoints.
4. 总体流程
- 使用 Protege 进行 本体（ontology）建模
- 根据本体建模，配置 RDF 与 关系数据库间的映射关系
- 导出 RDF
- 导入 Neo4j
参考：
Ontop 官网： https://ontop-vkg.org/ Ontop 仓库： https://github.com/ontop/ontop
