Indexing databases: All about their similarities and differences

Citation indexes, or, in other names, bibliographic indexes or bibliographic databases, serve a key role in listing and organizing journals and their articles, based on various factors ranging from disciplines, subjects, or even geographic regions (Nalen). According to Garfield (1970), Dhammi and Rehan-Ul-Haq (2016) formulated the following, slightly more restrictive definition: “Citation index (indexing) is an ordered list of cited articles, each accompanied by a list of citing articles. The citing article is identified as source and the cited article as reference. An abstracting and indexing service is a product, a publisher sells, or makes available. The journal contents are searchable using subject headings (keywords, author’s names, title, abstract, etc.) in available database.”

 Indexing Databases
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Due to the fact that journals need to go through a rather scrutinizing process to be recognized and included in a high-quality bibliographic database, indexed journals weigh more than those that are not (Walden University Library). In this article, we will provide a basic overview on indexing databases: after talking about their history, we list and categorize the most important ones.

The history of citation indexing and the science behind it today

Historical predecessors

According to Weinberg (1998), the invention of the citation index has a long history: before Shapiro detected a legal citation index published in 1743, it had been generally associated with Shepard (1873). However, today it is known that even 200 years earlier, such index was already included in the Talmud – which leads us to the conclusion that its first printed appearance as a Hebrew citation index, traces back to as early as 1511. However, as Weinberg pointed out, it is important to note that „the terms citation, quotation, reference, cross-reference, locator, and concordance are employed inconsistently in publications about Hebrew indexes. There is a lack of citation links between the secondary literature on Hebrew indexes and that of citation analysis.”

The birth of the new industry of indexing

According to Clarivate’s article on the history of citation indexing, there were three key factors that led to the rapid development of citation indexing in post-war US: 1, the need to manage information better; 2, the need to grow capacity in subject indexing for needs of individual researchers; and 3, the role of computerization in generating and compiling data. Dr Eugene Garfield, now Chairman Emeritus at Clarivate Analytics (previously ISI) founded, took part in, and optimized cutting edge research projects throughout the 1950s and 1960s, which have led to finding reliable methods to locate data and bring results to researchers’ inquiries across various disciplines.

Types and services of indexing databases

Today, the purposes of indexing databases are to give access to bibliometric data, as well as to provide research analytics results and improve performance. All databases are refreshed regularly, but there are differences in how often they insert updates. Note that each database system uses their own specific sets of indexed journals, hence altering scores (e.g., different citation numbers) are all valid and correct. Indexing databases are not to be mixed with aggregators, such as EBSCO, JStore, or ProQuest.

Indexing databases can be categorized by various features:

  • We can distinguish corporate services (like WoS, Scopus, Crossref, Google Scholar) from non-profit ones (e.g., SCImago, ERIH Plus, MathSciNet) that are creating indexes.
  • Some databases are selective on the basis of scientific excellence (WoS, Scopus, PubMed, ERIH Plus, ERIC), selective on ethical standards (DOAJ, Cabell) or are all inclusive (Crossref, Google Scholar, Research Gate).
  • Concerning the covered research fields, there are general (WoS, Scopus, ERIH PLUS, Crossref, Google Scholar), and subject specific databases (PubMed on medical research, and PsycINFO on psychology, ERIC on educational science, MathSciNet and ZblMATHon mathematics).
  • By access type, there are subscription based ones (WoS, Scopus, MathSciNet) as well as freely available platforms (SCImago, Google Scholar, Research Gate, ZblMATH).

The Zoo of indexing databases

But what do all the abbreviations in the section above stand for? How to make sense of database tables providing a large number of records and indexed columns, and how to retrieve records efficienty? Let us briefly outline a list of the most important indexing databases below, touching on details regarding their metrics, metrical parameters, their data structure, and rankings.

Web of Science (WoS)

WoS was founded by Eugene Garfield as a product of the Institute for Scientific Information. Currently it is owned by Clarivate. It includes many selective databases, ranging from general to subject-specific ones. It can only be accessed by subscription. Journal applications are made to WoS itself, which determines which database to add the journal into, on the basis of topical relevance. The most prestigious WoS category is the Core Collection, consisting of four subcategories:

  • Emerging Sources Citation Index (ESCI – since 2015)
  • Science Citation Index Expanded (SCIE – since 1964)
  • Social Science Citation Index (SSCI – since 1961)
  • Arts & Humanities Citation Index (AHCI – since 1975)

Their data are contained in the annually published, paywall protected Journal Citation Reports (JCR). The most respected journal metrics, provided to the journals in SCIE and SSCI, is the Journal Impact Factor (which means a certain average of citations per article). A few further metrical parameters are invented and published on a yearly basis; and ranking lists are composed within research domains.


Scopus is a product of Elsevier. It features a large database of academic journals from any research field. It is only accessible to the subscribers. The indexed journals are categorized by topic. Ranking lists, by several metrical parameters (the best known of them is perhaps Cite Score), are published annually.


SCImago is operated by a non-profit service of the Consejo Superior de Investigaciones Científicas (CSIC), University of Granada, Extremadura, Carlos III (Madrid) and Alcalá de Henares. It is freely accessible. It uses the data directly from Scopus, which means, the same journals are indexed. Applying this data, several metrical parameters, among them, Scimago Journal Rank (SJR) are calculated. Their ranking list within each Scopus subject category, provided by the SJR, is annually published, too. Note that the quartile in which a journal sits on this list is its widely used “Q-rank”.


PubMed is a service by the National Library of Medicine. The access to it is free. It is subject specific: only medical journals and books are added. It consists of three databases: MedLine, PubMed Central (PMC) and Bookshelf. PubMed is famous of being highly selective about the indexed content.


DOAJ is operated by the community interest company called Infrastructure Services for Open Access C.I.C. (is4oa). It is freely accessible. A strict criterion is that only Open Access journals are added (from any research field). However, the selection is based on research ethics and strict standards and the main aim is to promote research integrity.

Cabells list

Cabells list is a product by a private company founded by David W. E. Cabell. The services include Journalytics and Predatory Reports. It can only be accessed by subscription and is highly selective about the listed journals.


Crossref is run by a non-profit association, the Publishers International Linking Association Inc. (PILA). By nature, it is all inclusive (no selection is made based on quality or subject). Crossref registers data voluntarily provided by publishers.  Those are primarily the publishers who pay a reasonable fee. Some data is freely accessible (via basic search or API), more sophisticated analyses are available by subscription.

Google Scholar

Google Scholar is widely known and used, especially on undergraduate level. This database is run by Google. The access is free. While explains well how its ranking system works, perhaps the biggest disadvantage is that it provides no actual selection, which often results in irrelevant data.

How to get a journal indexed?

As stressed above, it is highly important for journals to be indexed. According to Clarivate and Scopus, there is a set of selection criteria to be considered, starting from technical requirements, through ethical aspects and transparency; furthermore, the composition of the given Editorial Board, the distribution and prestige of the authors, and, last but not least, the quality of the content itself, plus the significance and impact it brings. The application procedure is fully online (via a form). There is a possibility that the evaluation takes rather long, and it is also important to mention that in case of rejection, there is a re-application embargo. However, considering the value, it is without question worth the procedure.

Indexed titles at AKJournals

We are proud to say that the majority of our journals are indexed in some of the previously mentioned prestigious databases: our titles across various research fields, many of them Open Access, can be found at WoS, Scopus, SCImago, PubMed, DOAJ, CrossRef, PsycINFO, ERIH PLUS, and ERIC. For further reading, we recommend diving into related topics covered on our blog, such as the h-index and impact factor.


Content policy and selection. Elsevier.

Dhammi IK, & Rehan-Ul-Haq (2016) What is indexing. Indian Journal of Orthopaedics   50(2) pp. 115-6.

History of citation indexing. Clarivate.

Nalen, Z. C. What is a journal index, and why is journal indexation important? AJE Scholar.,public%20can%20search%20journal%20indexes

Walden University Library definition

Web of Science journal evaluation process and selection criteria. Clarivate.

Weinberg, B. H. (1998) The earliest Hebrew citation indexes in: Hahn, T. B. & Buckland, B. ed.: Historical Studies in Information Science. Asis (pp. 51-64.)