Truncation refers to the use of wildcard symbols, e.g. * or ?. Truncation symbols replace one or more letters and are most often placed at the end of your keywords. They can however also be placed in the middle of a keyword or, in some databases,  at the beginning of a keyword.

Truncation is especially good for finding the various grammatical forms of search terms, as well as alternative spellings, e.g. English and American, and for transcriptions of texts in other alphabets, e.g. Cyrillic or Arabic, etc.

You should use truncation with care. The location of the asterisk (*) has consequences. You could, for example, consider searching for the singular and plural forms independently instead. Then you will get exactly the word-end variations of the word you want. This can, in some databases, and within some subject areas (with precise specialist terminology), give better results.

Which characters you need to use, and how precisely they function will depend on the individual database. See under 'Help', or search tips, in the relevant base.

Masking is a specific form of truncation where you replace one single letter in a keyword with a masking symbol. Masking is usually used in the middle of a keyword:

Phrase search is used when you want to ensure the database searches for precisely the text you have written. You can do this by placing one or more words in quotation marks. Phrase search is particularly good for composite terms.

Here you will find only references which contain the precise term: "solar energy". A search without quotes will, in many databases, be treated as a search for solar AND energy, where both terms must be present but not necessarily stand together and in that order.

Proximity operators are used to indicate the maximum distance (in number of words) that can exist between your search terms. The use of proximity operators can provide you with more flexibility and control in your searches.

This will find references where the word cognitive appears a maximum of 2 words distance away from the word therapy. This means the search will also catch words and sentences such as ”cognitive behavioural therapy” and ”therapy with cognitive behavior treatment”.

Your keywords are crucial in determining what you find.  It is therefore worth spending time on finding the best keywords. In many databases, you need to consider whether you want to carry out a full-text search, or whether you want to search using controlled subject terms.

Controlled subject terms

Controlled subject terms are the "pre-selected" keywords the database owners have attached to the individual references to denote what a document "is about". 

The controlled subject terms are selected from a controlled vocabulary. They ensure that you can create consistent subject searches, as references on the same subject can then be found with the precise same keyword, irrespective of the wording in titles and abstracts.

The controlled subject terms vary from database to database, and you cannot expect a search term used as a controlled keyword in one database to be found as a controlled subject term in another database.

The list of controlled subject terms may be hierarchically organised into a thesaurus. Here you can choose between more generalized broader terms (BT) or more specific narrower terms (NT). Thesauri are mainly found in the fields of medicine, psychology and the natural sciences,  and education.

Full-text search

When you do a full-text search, you search for words in titles, abstracts, notes and keywords, etc. It is therefore important to find all possible and relevant keywords, as well as variations thereof. In other words you need to be creative and consider all possible synonyms, close synonyms, related terms, narrower/broader terms, antonyms, abbreviations, grammatical or linguistic variations of your keywords.

It is important, especially when searching across disciplines that you do not lock yourself in to the terminology of your own particular field, but also "translate" your terms to those found in other subject terminologies.

When you make a free text search it can vary as to which fields the individual database actually incorporates into the search. Some databases include the reference list, or the full text of the publication. In order to specify a search, you can use field searching. When doing a keyword search you could, for example, narrow your search to only search through titles or abstracts. Example from the database Pubmed:

This gives a search result where the phrase "patient education" appears either in the title or the abstract.

Field searches can also be used to scan through some very specific fields such as ”Geographic Terms”, ”CompanyEntity” or ”Conference location”, thus minimising non-relevant results in your search.

Should I choose full-text search or use controlled subject terms?

If you need to find "everything" on a particular subject, for a systematic review for instance, then you will need to use both controlled subject terms and full-text search. But in other cases there may be a good argument for choosing one or the other approach, depending on what you are working with. Generally speaking, you can say:

• A search on controlled subject terms will give fewer, but much more precise results.
• Full-text search will give many more search results, but also a lot of "noise" (i.e. non-relevant references).
• If you work within a field where the terminology is consistent, it may be a good idea to use the controlled subject term.
• If you are working in a field with changeable or ambiguous terminology, or if your work is multidisciplinary in nature, it may be an advantage to carry out full-text searches.

A combined search, where you search across multiple databases with multidisciplinary coverage can have its own advantages, especially if your work is itself multidisciplinary in nature.

Combined searches can be performed in the large database hosts such as Ebsco and ProQuest, where you can easily select the individual databases that you want to include in your search.

Combined searches can also be very good in the initial phases of your searching in order to find the best databases for your subject area.

• The advantage of combined search is that you can easily cover a large amount of literature.
• The disadvantage is that the precision in your searches suffers somewhat as you cannot use the individual database’s specialised search fields and controlled subject terms.

Google, and particularly Google Scholar, is used by many researchers as a first stop when making literature searches. In the initial phases this can be fine. However, we cannot recommend Google Scholar for systematic literature searches for the following reasons:

• Large quantities of academic literature is not freely accessible on the internet and is therefore not indexed by Google. You are only searching the "tip of the iceberg" - as opposed to the bibliographic databases.
• The basis for the data available is unclear, and you have no way of knowing what is included in the 'Database' and what is not included. This also makes it difficult for others (and you) to reconstruct your searches at a later point in time.
• Obsolete information is mixed with new, relevant information. Similarly, there can also often be several versions of the same article (for example, preprints, postprints, publishers’ print edition, etc.), which can sometimes be an advantage, but which also requires that you need to make sure to get the latest version.

The search mechanism behind Google Scholar can, however, be very useful when it comes to finding similar articles and finding several versions of the same document (in those cases where this is relevant). You can also use Google Scholar to find full-text versions of articles, either via AU Library's subscriptions or as Open Access.

Google Scholar is a good tool for verifying references, and you could potentially use it as supplement to citation searches in Web of Science and Scopus. Often you get different citations in Google Scholar than in Web of Science and Scopus (which database provides most hits will vary according to subject area and the specific keywords chosen).

Read more about Google Scholar:

• https://scholar.google.dk/intl/en/scholar/about.html 
• https://scholar.google.dk/intl/en/scholar/help.html