Document Classification Using Multiscale Text Fingerprints

A server computer system comprising at least one processor configured to perform transactions with a plurality of client systems, wherein a transaction comprises:

• receiving a text fingerprint from a client system of the plurality of client systems, the text fingerprint determined for a target electronic document so that a length of the text fingerprint is constrained between a lower bound and an upper bound, wherein the lower and upper bounds are predetermined;
• and
• sending to the client system a target label indicative of a category of documents that the target electronic document belongs to,
• wherein determining the text fingerprint comprises:
• selecting a plurality of text tokens of the target electronic document;
• in response to selecting the plurality of text tokens, determining a fingerprint fragment size according to the upper and lower bounds, and according to a count of the selected plurality of text tokens;
• determining a plurality of fingerprint fragments, each fingerprint fragment of the plurality of fingerprint fragments determined according to a hash of a distinct text token of the selected plurality of text tokens, each fingerprint fragment consisting of a sequence of characters, a length of the sequence chosen to equal the fingerprint fragment size;
• and
• concatenating the plurality of fingerprint fragments to form the text fingerprint,
• and wherein determining the target label comprises:
• retrieving a reference fingerprint from a database of reference fingerprints, the reference fingerprint determined for a reference electronic document belonging to the category, the reference fingerprint selected according to a length of the reference fingerprint so that the length of the reference fingerprint is between the upper and lower bounds;
• and
• determining whether the target electronic document belongs to the category according to a result of comparing the text fingerprint to the reference fingerprint.

A method comprising employing at least one processor of a client computer system to determine a text fingerprint of a target electronic document so that a length of the text fingerprint is constrained between a lower bound and an upper bound, wherein the lower and upper bounds are predetermined, and wherein determining the text fingerprint comprises:

• selecting a plurality of text tokens of the target electronic document;
• in response to selecting the plurality of text tokens, determining a fingerprint fragment size according to the upper and lower bounds, and according to a count of the selected plurality of text tokens;
• determining a plurality of fingerprint fragments, each fingerprint fragment of the plurality of fingerprint fragments determined according to a hash of a distinct text token of the selected plurality of text tokens, each fingerprint fragment consisting of a sequence of characters, a length of the sequence chosen to equal the fingerprint fragment size;
• and
• concatenating the plurality of fingerprint fragments to form the text fingerprint.

A method comprising employing at least one processor of a server computer system configured to perform transactions with a plurality of client systems, to:

• receive a text fingerprint from a client system of the plurality of client systems, the text fingerprint determined for a target electronic document so that a length of the text fingerprint is constrained between a lower bound and an upper bound, wherein the lower and upper bounds are predetermined;
• and
• send to the client system a target label determined for the target electronic document, the target label indicating a category of documents that the target electronic document belongs to,
• wherein determining the text fingerprint comprises:
• selecting a plurality of text tokens of the target electronic document;
• in response to selecting the plurality of text tokens, determining a fingerprint fragment size according to the upper and lower bounds, and according to a count of the selected plurality of text tokens;
• determining a plurality of fingerprint fragments, each fingerprint fragment of the plurality of fingerprint fragments determined according to a hash of a distinct text token of the selected plurality of text tokens, each fingerprint fragment consisting of a sequence of characters, a length of the sequence chosen to equal the fingerprint fragment size;
• and
• concatenating the plurality of fingerprint fragments to form the text fingerprint,
• and wherein determining the target label comprises:
• retrieving a reference fingerprint from a database of reference fingerprints, the reference fingerprint determined for a reference electronic document belonging to the category, the reference fingerprint selected according to a length of the reference fingerprint so that the length of the reference fingerprint is between the upper and lower bounds;
• and
• determining whether the target electronic document belongs to the category according to a result of comparing the text fingerprint to the reference fingerprint.