in wordpress, the attachment is saved in the same table as the article, but all the information in the attachment is saved according to the following format. Why this format?

by the way, how did this format come from?

a:5:{s:5:"width";i:800;s:6:"height";i:600;s:4:"file";s:15:"laravelsite.png";s:5:"sizes";a:4:{s:9:"thumbnail";a:4:{s:4:"file";s:23:"laravelsite-150x150.png";s:5:"width";i:150;s:6:"height";i:150;s:9:"mime-type";s:9:"image/png";}s:6:"medium";a:4:{s:4:"file";s:23:"laravelsite-300x225.png";s:5:"width";i:300;s:6:"height";i:225;s:9:"mime-type";s:9:"image/png";}s:12:"medium_large";a:4:{s:4:"file";s:23:"laravelsite-768x576.png";s:5:"width";i:768;s:6:"height";i:576;s:9:"mime-type";s:9:"image/png";}s:14:"post-thumbnail";a:4:{s:4:"file";s:23:"laravelsite-800x510.png";s:5:"width";i:800;s:6:"height";i:510;s:9:"mime-type";s:9:"image/png";}}s:10:"image_meta";a:12:{s:8:"aperture";s:1:"0";s:6:"credit";s:0:"";s:6:"camera";s:0:"";s:7:"caption";s:0:"";s:17:"created_timestamp";s:1:"0";s:9:"copyright";s:0:"";s:12:"focal_length";s:1:"0";s:3:"iso";s:1:"0";s:13:"shutter_speed";s:1:"0";s:5:"title";s:0:"";s:11:"orientation";s:1:"0";s:8:"keywords";a:0:{}}}