## 3 Results from Patent Data Mining across the Countries
### IPCs and the Patent Data Pre-processing: The Basis  
In this phase, the datasets of the patents for inventions from the 'technological power' countries are featured and stored in a data repository. For the purposes of knowledge discovery, all of the patents in sections G (which covers physics-related patents such as those for technologies involving optics, data storage, image processing, magnetic materials, etc.) and H (which covers electricity-related patents such as those for technologies involving electronic circuits, electrical communication, semiconductor components, etc.) during the 2007-2015 period included in the official patent databases of the top 9 high-tech patenting countries are focused on. The 'technological powers' whose patent databases are selected from include the United States (USA), Japan (JPN), Germany (GER), Great Britain (GBR), South Korea (KOR), China (CHN), Canada (CAN), Taiwan (TWN) and the European Union (EU). For a special style to apply a patent in some countries in EU, see the supplementary discussion in Appendix C.  
Consistent with previous works on patent indicator frameworks (see Sections 2.1 and 2.2), this study utilizes the IPC codes of these patents. This is not only because IPC is a common code field for each patent in all the patent databases investigated herein, but also because it connotes the 'technological classification' by which to index the given patent per se. Therefore, it should provide a suitable shared foundation for the desired analytical works. According to the Strasbourg Agreement of 1971, every patent should at least receive an IPC. The possibly tagged IPC codes are alpha-numerically coded and they are organised systematically in a hierarchical structure. This means that each patent is classified into suitable categories. At the root of the hierarchy, each patent is assigned a'section', which is indicated by a letter from set {'A', 'B',..., 'H'} [9]. Following the section tag, there are two numerical digits coding the 'class' of the patent, followed by some'subclass' coded in terms of another capitalised letter. The entire 'class-subclass' tag is then followed by another tag of 'group-subgroup' codes. With the standard of IPC, 1-3 numerical digits are allowed to code the 'group', while 2-4 are allowed to code the'subgroup'. Figure 3 illustrates this coding scheme. As shown, the hierarchy entails, in fact, a tree of 5 levels extending above the root, and the set of all possible IPC codes is obtained by tree traversal. Note that in this figure, only the section names are shown; names for the codes in the rest of the layers are omitted to allow for simplicity in the presentation. For illustration purposes, Figure 3 also demonstrates a specific IPC code: \"G11C 13/04\". Parsing it according to the hierarchy, this is a patent in the \"11: information storage\" class and \"C: static storage device\" subclass within the \"G: physics\" section. In an additional detail, the postfix of this IPC code is \"13/04\". This means, for a patent that is tagged with this group/subgroup code, that the technology in question is related to \"digital storage memory by using optical components\". Therefore, the entire IPC sequence is interpreted as \"optical-components-enabled static data memory device under the physics  
Figure 3: The coding style of IPC using the “G11C 13/04” code as an example. section\", which is a relatively long description. This explains why the shortened IPC coding style is used. The full compilation of the IPC codes can be accessed via the official website of the WIPO [22]. For this study, the IPC coding style forms a 'natural taxonomy' that is useful because the patents which receive the same (full) IPC code are highly related to one another. Furthermore, patents that receive the same 'code prefix' can also be supposed to be related to some extent. This study utilizes this feature of the coding style. That is, using different'resolutions' to view the IPC codes can determine the 'granularity' of the patent data pre-processing for the subsequent analyses.