Entrez Global Query

query can be parsed differently in each database, depending on the search fields a particular database has and how it is indexed.

example 1, search for: presenilin 1 (without quotes) and view the "Details" on the search results pages of the PubMed, Nucleotide, Structure, and Genome Project databases. Note that extranneous, unrelated hits are found in Structure and Genome Project. So when evaluating search results from Global Query, it is helpful to be familiar with the scope and purpose of the various Entrez databases, and to have some understanding of the differences in which they might be indexed.

example 2, search for: human colon cancer (without quotes) and view the "Details" on the search results pages of the PubMed, Nucleotide, Structure, and Genome* databases. In the Genome database in particular, note that the query was parsed in a logical way, but the search engine is not picking up some genome records, such as human, mouse, and rat chromosomes, that have genes associated with colon cancer. Why? Because records in the Entrez Genome database are indexed at the overall genome/chromosome level, and their biological annotations such as genes are not necessarily indexed. The Genes database indexes at that level, or a user would have to search for genes within individual genomes through Map Viewer (for higher organisms) or through the Entrez Genomes "search for gene" function that is available in the graphic display of a lower organism's genome.
*Entrez Genome is a separate database from Entrez Genome Project. We will discuss these databases in more detail in the Genomes module of the course. For now, we are just pointing them out so you can see the differences in how various Entrez databases are indexed and searched. The NCBI Resource Guide also provides a description of both databases and the differences between them.

if the number of hits in a particular database is in a grey box, that is an indicator that the search did not work as anticipated

for example, perhaps one or more of the query terms was not found, so only the other terms were searched

not all search fields are available in all databases, so if field specifiers are used in a complex Boolean query, the search engine will convert the search to "All Fields" in any database that lacks the specified field

example 3: search for PSEN1[gene] and note that PubMed Central search results are shown in a grey box; the Details page indicates that the [gene] field is not found in that database and shows the system searched "All Fields" instead

Entrez		Revised 10/31/2007