Fable
The relay station alliance handed the trouble of choosing horses to the main station
There were more than a dozen stations on the post road, and each station raised its own horses, set its own fodder standards, and arranged its own shifts. Life at a small station was simple: a letter comes, bring a horse, go. But once the merchant guild grew large, problems appeared.
The horses at each station varied in quality, and finding old letters also relied on the station master's memory. When a merchant asked "is there an old contract similar to this one," Station A searched by place name, Station B by customer, and Station C rummaged for a long time but still could not say for sure. The more letters there were, the slower it became to find similar content.
The chamber of commerce first required each station to compile a thicker index. An index could look up exact names, but it struggled with requests that were similar in meaning. The second fix was to let the old postman recommend based on experience, but experience was useful yet could not support the growth of the whole chamber of commerce.
Later the chamber of commerce built a central station specifically to store each letter's feature tags and organize the horse routes by similarity. Each relay station sent new letters for registration, and during queries the central station quickly found the closest batch of old letters and returned them to each station for use.
The main station is also responsible for scaling, backup, partitioning, and speed. Small relay stations do not need to raise complex horse herds themselves, nor study how to find similarities in massive piles of old letters; they only need to submit tags, check tags, and retrieve results according to the agreement.
The chamber of commerce finally turned finding similar old cases into a stable capability. The station master understood that some infrastructure isn't just for storing things, but is specifically responsible for efficiently preserving, indexing and recalling similar content, so that upper-layer businesses don't have to repeatedly build their own.
The main station also maintains the roads. If certain feature signs grow too fast, it partitions them; if certain queries slow down, it rebuilds the paths; if requests at a station surge, it expands the horse lanes. What a small relay station sees is one query, but behind it is a whole set of ongoing operations.
Later, the merchants’ association compared the cost of building its own system with using the central station. Keeping their own horses was enough for a few dozen letters. Once the letters became an ocean, with fast searches and high reliability required, the specialist station proved its value. Teams could focus on business rather than the mechanics of finding routes. The station also made new ventures easier to try. When the association opened a new shop, it could join the existing letter network through agreed registration and query procedures, without first building a complete archive. Stable shared capabilities made changes in the services above them easier. The more reliable the station became, the more each branch could focus on the letters themselves and its commitments to customers. That was also why the station charged a fee: it sold continuously available similarity search, rather than stables.