A physical object is a concrete representation or storage unit for part or all of a logical object. A library copy can represent a book, while an encyclopedia volume represents only a subset of the complete encyclopedia. section 8.2 section 7.1
Physical objects clarify how logical things are stored and managed:
- Multiple physical objects may represent one logical object, as with replicated copies. section 8.2
- Disjoint physical objects may partition one logical object across components or nodes. section 7.1 section 7.2
- Placement rules make physical objects findable, but uneven demand and cross-references create operational challenges. section 7.1
SICP editions and copies
A library holds copies of several SICP editions. Whether a copy counts depends on which logical book the reader considers equivalent: any edition, Scheme editions, or the JavaScript edition. section 8.2
Table 8.1 Book editions
| Name |
Edition |
Year |
| SICP |
First |
1984 |
| SICP |
Second |
1996 |
| SICP |
JavaScript |
2022 |
Compare the editions that make the distinction between logical identity and physical copies concrete. section 8.2
