KB is a collection of records in database. Records are often stored as triples in the form subject predicate object.
Collections of records / triples from difference sources with different naming schemes are counted as Combined Data, which is discussed in Section 2.1.3.
Freebase里的数据格式：
一些常用的KB数据库：
Data Formats：
KB数据通常保存为RDF的格式。序列化后，可以用下面的形式保存：
N-triples
N-quads
TSV
Turtle
2.1.3 Combined Data
可以将Text和KB进行结合，也可以将多个KB进行结合。
combined data的两个原则：
link: link a text to a knowledge base by recognizing mentions of entities from the knowledge base in the text and linking to them。这里涉及到NER和disambiguation的任务。
mult: combine multiple knowledge bases with different naming schemes (such that the same entity or relation may exist with different names)
Commonly Used Datasets：
Text Linked to a Knowledge Base：
将link边骂道text中的格式是XML。下面是Wikipedia LOD的一个例子：
Semantic Web：
The data from the Semantic Web is often also called linked open data (LOD), because contents can be contributed and interlinked by anyone, just like web pages (but in a different format, see below). 我们将这种数据叫作semantic web data，它符合combining data的两个原则：
link: provided by semantic markup for ordinary web pages.
mult: anyone can contribute + absence of a global schema.
Summary:
这是一篇关于语义检索的survey，详细介绍了关于语义检索的各种范式，设计到的NLP任务，以及基于Text和基于KB的不同方法。
FTIR: Foundations and Trends in Information Retrieval
Resource:
Paper information:
Notes:
2 Classification by Data Type and Search Paradigm
2.1 Data Types and Common Datasets
2.1.2 Structured Data / Knowledge Bases
KB is a collection of records in database. Records are often stored as triples in the form subject predicate object.
Collections of records / triples from difference sources with different naming schemes are counted as Combined Data, which is discussed in Section 2.1.3.
Freebase里的数据格式：
一些常用的KB数据库：
Data Formats：
KB数据通常保存为RDF的格式。序列化后，可以用下面的形式保存：
2.1.3 Combined Data
可以将Text和KB进行结合，也可以将多个KB进行结合。
combined data的两个原则：
Commonly Used Datasets：
Text Linked to a Knowledge Base：
将link边骂道text中的格式是XML。下面是Wikipedia LOD的一个例子：
Semantic Web：
The data from the Semantic Web is often also called linked open data (LOD), because contents can be contributed and interlinked by anyone, just like web pages (but in a different format, see below). 我们将这种数据叫作semantic web data，它符合combining data的两个原则：
其中“mult”原则可以被RDF实现，可以把任意的文本链接到RDF的数据上。比如下面关于法国城市Emburn的例子。主要前缀 rdf: 和 gn: 可以让内容更紧凑，方便我们阅读：
“link”原则可以通过semantic markup来实现。比如下面是一个HTML页面，使用了Microdata markup：
下面是4个最常用的semantic markup。前3个直接使用HTML tags。而JSON-LD比其他3个的优势在于，可以更清晰地分割开ordinary content和semantic content：
2.2 Search Paradigms
2.2.1 Keyword Search
2.2.2 Structured Search
2.2.3 Natural Language Search
3 Basic NLP Tasks in Semantic Search
TODO
4 Approaches and Systems for Semantic Search
4.2 Structured Search in Knowledge Bases
4.2.1 Basic Techniques
两种保存KB的方法：保存到standard relational database management system (RDBMS)，或者triple store。后者在4.2.2部分介绍。
如果是保存到RDBMS，query是SPARQL，那么query可以被转换为SQL queries.
Performance：
Dedicated triples stores 比 RDBMS 有优势。比如可以使用针对triple数据特化的index data structure。但是，RDBMS在处理complex query方面也有优势。
4.2.2 Systems
到2016年为止，3个最常用的系统是：Virtuoso，Jena， Sesame。
4.3 Structured Data Extraction from Text