This field is used to link sub-records (the contents of collectaneous works) to main records (the main title). The structure of the link is 2-letter operator code followed by 3-digit running number. The presence of the operator code is designed to ensure that the link is unique: when assigning a link, each operator should check the index and assign the next available running number under his own code. The sub-records are then numbered serially, following a plus + sign. The linking structure is best understood by studying the following example:
#0rx dh001 己卯叢編 / (民國)趙詒琛, (民國)王大隆編
#0rx dh001+1 逸禮大義論 六卷 / (清)汪宗沂撰
#0rx dh001+2 靖康稗史 / (宋)耐菴編
#0rx dh001+2+1 宣和乙巳奉使金國行程錄 一卷 / (宋)佚名撰
#0rx dh001+2+2 甕中人語 一卷 / (宋)韋承撰
#0rx dh001+2+3 開封府狀 一卷 / (宋)佚名撰
#0rx dh001+2+4 南征錄彙 一卷 / (金)李天民編
#0rx dh001+2+5 青宮譯語節本 一卷 / (金)王成棣撰
#0rx dh001+2+6 呻吟語 一卷 / (宋)佚名撰
#0rx dh001+2+7 宋俘記 一卷 / (金)可恭撰
#0rx dh001+3 行人司重刻書目 不分卷 / (明)徐圖等撰
#0rx dh001+4 梵麓山房筆記 六卷 / (清)王汝玉撰
If there are 10 or more sub-records, they should be numbered +01, +02, &c to ensure that the links are indexed in the correct order:
#0rx dh014+09
#0rx dh014+10
#0rx dh014+11
&c
Similarly, if there are 100 or more, they should be numbered +001 &c:
#0rx sn002+099
#0rx sn002+100
#0rx sn002+101
&c
If a sub-record itself has further sub-records, another sequence is formed following another plus sign, as in the above example of a complete linked record set. This process can continue for as many levels as might be required.
When a main record is retrieved, the program uses the link to identify and display all the sub-records attached to it. When a sub-record record is retrieved, the program uses the link to identify and display the main record of which it is part