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: Patent retrieval: a literature review 
Chapter Title:  Introduction 
1. Abstract of Cited Paper (BIB001):  The patent system is designed to encourage disclosure of new technologies and novel ideas by granting exclusive rights on the use of inventions to their inventors, for a limited period of time. Before a patent can be granted, patent o ces around the world perform thorough searches to ensure that no previous similar disclosures were made. In the intellectual property terminology, such kind of searches are called prior art searches. In some industries, the number of granted patents a company owns has a high impact on the market value of the company. This underlines the importance of well-performed prior art searches. Together with the Trec Chem track [5], also organized by our institution, the Clef Ip e ort comes to complete the work that is being done in the series of Ntcir workshops (see for example [4]). The rst Clef Ip track ran within Clef 2009. The purpose of the track was twofold: to encourage and facilitate research in the area of patent retrieval by providing a large clean data set for experimentation; to create a large test collection of patents in the three main European languages for the evaluation of cross lingual information access. The Clef Ip data set includes documents published by the European Patent O ce (Epo) which contain a mixture of English, German and French content. The track focused on the task of prior art search. In 2010 and 2011, the Clef Ip track was organized as a benchmarking activity (lab) in the Clef conference. In these years, the main goal of the Clef Ip e ort remained the same to foster research in the patent retrieval area, and provide a large clean data set. To this end, the number of tasks in the track was increased and the data set was enlarged. Recognizing the importance of patent classi cations in the daily activity of an intellectual property professional, in 2010 the Clef Ip benchmarking activity included a patent classi cation task. The participants were asked to classify 
2. Abstract of Cited Paper (BIB002):  Intellectual property in the form of patents plays a vital role in today's increasingly knowledge-based economy. This book assembles state-of-the art research and is intended to illustrate innovative approaches to patent information retrieval. 
3. Abstract of Cited Paper (BIB003):  Sixteen years ago, two of us published the first detailed empirical look at patent litigation. In this Article, we update and expand the earlier study with a new hand-coded data set. We evaluate all substantive decisions rendered by any court in every patent case filed in 2008 and 2009 — decisions made between 2009 and 2013. We consider not just patent validity but also infringement and unenforceability. Moreover, we relate the outcomes of those cases to a host of variables, including variables related to the parties, the patents, and the courts in which those cases were litigated. The result is a comprehensive picture of the outcomes of modern patent litigation, one that confirms conventional wisdom in some respects but upends it in others. In particular, we find a surprising amount of continuity in the basic outcomes of patent lawsuits over the past twenty years, despite rather dramatic changes in who brought patent suits during that time. 
4. Abstract of Cited Paper (BIB004):  In this comprehensive new study, we evaluate all substantive decisions rendered by any court in every patent case filed in 2008 and 2009 — decisions made between 2009 and 2013. We assess the outcome of litigation by technology and industry. We relate the outcomes of those cases to a host of variables, including variables related to the parties, the patents, and the courts in which those cases were litigated. We find dramatic differences in the outcomes of patent litigation by both technology and industry. For example, owners of patents in the pharmaceutical industry fare much better in dispositive litigation rulings than do owners of patents in the computer & electronics industry, and chemistry patents have much greater success in litigation than their software or biotech counterparts. Our results provide an important window into both patent litigation and the industry-specific battles over patent reform. And they suggest that the traditional narrative of industry-specific patent disputes, which pits the IT industries against the life sciences, is incomplete.

Literature Review:
Patents represent proxies for economic, technological, and even social activities. The Intellectual Property (IP) system motivates the disclosure of novel technologies and ideas by granting inventors exclusive monopoly rights on the economic value of their inventions. Patents, therefore, have a major impact on enterprises market value BIB002 . With the continuous rise in the number of filed patent applications every year, the need for effective and efficient systems for managing such tremendous amounts of data becomes inevitably important. Typical patent analysis tasks include: (1) technology exploration in order to capture new and trendy technologies in a specific domain, and subsequently using them to create new innovative services, BIB004 technology landscape analysis in order to assess the density of patent filings of specific technology, and subsequently direct R&D activities accordingly, BIB005 competitive analysis and benchmarking in order to identify strengths and differences of corporate's own patent portfolio compared to other key players working on related technologies, (4) patent ranking and scoring in order to quantify the strength of the claims of an existing or a new patent, and (5) prior art search in order to retrieve patent documents and other scientific publications relevant to a new patent application. All those patent-related activities require tremendous level of domain expertise which, even if available, must be integrated with highly sophisticated and intelligent analytics that provide cognitive and interactive assistance to the users. Patent retrieval (PR) is the pillar of almost all patent analysis tasks. PR is a subfield of Information Retrieval (IR) which is concerned with developing techniques and methods that effectively and efficiently retrieve relevant patent documents in response to a given search request. Although the field of IR has received huge advances from decades of research and development, research in PR is relatively newer and more challenging. On the one hand, patents are multi-page, multi-modal, multi-language, semi-structured, and metadata rich documents. On the other hand, patent queries can be a complete multi-page patent application. These unique features make traditional IR methods used for Web or ad hoc search inappropriate or at least of limited applicability in PR. Moreover, patent data are multi-modal and heterogeneous. As indicated by Lupu et al. BIB003 , analyzing such data is a challenging task for many reasons; patent documents are lengthy with highly complex and domain-specific terminology. To establish their work novelty, inventors tend to use jargon and complex vocabulary to refer to the same concepts. They also use vague and abstract terms in order to broaden the scope of their patent protection making the problem of patent analysis linguistically challenging. PR starts with a search request (query) which often represents a patent application under novelty examination. Therefore, several methods for query reformulation (QRE) have been proposed in order to select, remove, or expand terms in the original query for improved retrieval. QRE methods are keyword-based, semantic-based, or interactive. Keyword-based methods work by searching for exact matches between search query terms and the target corpus, and thus fail to retrieve relevant documents which use different vocabularies but have similar meaning to the reformulated query. In order to alleviate the vocabulary mismatch problem, semantic-based methods try to search by meaning through expanding queries and/or target corpus with similar or related terms and thus bridging the vocabulary gap. Because neither method proved acceptable performance, few interactive methods were proposed to allow users to interactively control QRE with reasonable effort. This review aims to provide researchers with an illustrative and critical overview of recent trends, challenges, and opportunities in PR. The rest of this paper is organized as follows. Section 2 presents some preliminaries and background about patents data. Section 3 provides an overview of evaluation tracks and data collections for PR benchmarking. An illustration of PR tasks is presented in Sect. BIB001 . Section 5 presents a comprehensive review on PR methods and approaches. Section 6 lightly touches on related tasks such as patent quality assessment, litigation, and licensing. Finally, concluding remarks are presented in Sect. 7.