A database in which search formulas can be assembled in the search history

1.Document type selection.

On the literature query page, "Document Type Selection" lists the various types of literature databases that can be queried by users in this system. This is a required item and can be single, multiple, or all. The system has a cross-database search function, which can search documents in multiple databases at the same time.

2.Select the query scope.

This is a radio choice item. You can select any one of the items such as author, title, abstract, keyword, classification number, or full-text search to determine that the system will search the corresponding fields in the database. The Full-Text Search option searches all fields in the database.

3.Query the selection of the age limit.

Used to select the year of publication of the document to be searched. The selected year is equivalent to January 1 to December 31 of the current year, and the default time is all years.

4.Enter a search term.

You can enter a single word closely related to the query topic for search, or you can combine it with "and", "or", and "not" to form a more complex logical search query. For example, if you want to find ** about computer-aided design, you can use the Chinese phrase "computer-aided design" or the English abbreviation "cad" to express, through the relationship of "or", you can form such a search query: computer-aided design or cad After entering the search conditions, press the "search" button to query the bibliographic list of related literature.

Hello, the commonly used retrieval system for retrieving the required information from a database is the catalog retrieval system. According to the function of retrieval, it can be divided into bibliographic retrieval system and factual manual data retrieval chain comma system. The bibliographic retrieval system is mainly to search for relevant contributions to a research topic, and the result is to obtain clues to the relevant literature of a complete call, and the object of the retrieval operation is the retrieval tool.

Fact data retrieval systems are used to retrieve various facts or data.

It is a search method that restricts the search term to one or several fields in a database record. Here's how:

Answer]: BThe three relational operations involved in retrieving the operation of pure group operations in the relational database include selection, orange projection and joining; The comparison in option b) is not part of the pant hood relationship operation.

Answer]: Thing does B

The relational operations used in the query expression in the query process are: selection, projection, and join.

Selection: The act of finding a tuple from a relationship pattern that satisfies a given condition is called selection.

Projection: Specifying several attributes from a relationship pattern to form a new relationship is called a projection.

Connection: Occlusion splices two relationship patterns into a wider relationship pattern macrocrack, and generates a new relationship that contains tuples that meet the conditions.

Answer]:bb) [Analysis] The internal mode, also known as the physical mode, gives the structure and physical access method of the physical storage cluster of the data seepage library, such as the file structure, index, cluster and hash of the data blind storage, and the physical nature of the internal mode is mainly reflected in the operating system and file level, and it has not yet penetrated into the device level (such as disk and disk operation).

The data class data slag library can retrieve all the pinkai data. （）

a.Correct as a bucket rock.

b.Mistake. Correct answer: B