A "consultable" object. This is an inanimate object that can be consulted about various topics, almost the way an actor can be asked about topics. Examples include individual objects that contain voluminous information, such as books, phone directories, and maps, as well as collections of individual information-carrying objects, such as file cabinets or bookcases.

A consultable keeps a database of TopicEntry objects; this works in much the same way as the topic database system that actors use. Create one or more ConsultTopic objects and place them inside the Consultable (using the 'location' property, or using the '+' syntax). When an actor consults the object about a topic, we'll search our database for a ConsultTopic object that matches the topic and is currently active, and show the response for the best one we can find.

From an IF design perspective, consultables have two nice properties.

First, they hide the boundaries of implementation, by letting the game *suggest* that there's an untold wealth of information in a particular book (or whatever) without the need to actually implement all of it. We only have to show the entries the player specifically asks for, so the game never has to admit when it's run out of things to show, and the player can never know for sure that there's not more to find. Be careful, though, because this is a double-edge sword, design-wise; it's easy to abuse this property to hide information gratuitously from the player.

Second, consultables help "match impedances" between the narrative level of detail and the underlying world model. At the narrative level, we paint in fairly broad strokes: when we visit a new location, we describe the *important* features of the setting, not every last detail. If the player wants to examine something in closer detail, we zoom in on that detail, assuming we've implemented it, but it's up to the player to determine where the attention is focused. Consultable objects give us the same capability for books and the like. With a consultable, we can describe the way a book looks without immediately dumping the literal contents of the book onto the screen; but when the player chooses some aspect of the book to read in detail, we can zoom in on that page or chapter and show that literal content, if we choose.

Also, note that we assume that consultables convey their information through visual information, such as printed text or a display screen. Because of this, we by default require that the object be visible to be consulted. This might not be appropriate in some cases, such as Braille books or talking PDA's; to remove the visual condition, override the pre-condition for the Consult action.

class Consultable :   Thing   TopicDatabase