譯文：

很多用戶遇到的問題是可伸縮性。當(dāng)項(xiàng)目模型在實(shí)際使用的時(shí)候變得非常大時(shí)，就會(huì)遇到可伸縮性的問題。當(dāng)運(yùn)行變得遲鈍，哪怕很小規(guī)模的運(yùn)行也會(huì)非常費(fèi)力。建筑模型用掉了電腦很多內(nèi)存空間。大型建筑會(huì)包含上百萬個(gè)不同形狀的構(gòu)件?？缮炜s性同時(shí)受建模規(guī)模（比如樓層面積）和模型中的詳細(xì)程度影響。即使在一個(gè)簡(jiǎn)單的建筑中，如果對(duì)每個(gè)釘子和螺絲都建模，也會(huì)出現(xiàn)可伸縮性問題。

參數(shù)化建模整合了設(shè)計(jì)規(guī)則，即將某一構(gòu)件的形狀和參數(shù)關(guān)聯(lián)到另一個(gè)構(gòu)件的形狀和參數(shù)中。這些規(guī)則形成了關(guān)系層次：構(gòu)件內(nèi)參數(shù)化關(guān)系、構(gòu)件間參數(shù)化關(guān)系，根據(jù)另一個(gè)構(gòu)件的變化調(diào)整某一構(gòu)件的形狀，控制軸網(wǎng)和控制曲面之間的層次關(guān)系決定了形狀的參數(shù)和一組相關(guān)聯(lián)構(gòu)件的放置。雖然構(gòu)件內(nèi)和構(gòu)件間的參數(shù)化關(guān)系是構(gòu)件的局部更新，但是這種層次規(guī)則的擴(kuò)散可更新整個(gè)模型。局部參數(shù)化規(guī)則擴(kuò)散只在模型上產(chǎn)生合理要求，然而某些系統(tǒng)架構(gòu)卻限制了管理這種大批量層次規(guī)則傳播的能力。同樣，把項(xiàng)目分成若干部分來開展的同時(shí)仍然管理大批量層次關(guān)系是很困難的。

問題就在于內(nèi)存大小。所有構(gòu)件形狀方面的運(yùn)行都必須占用內(nèi)存。管理參數(shù)化更新的一個(gè)簡(jiǎn)單方法就是把項(xiàng)目存儲(chǔ)在內(nèi)存中。如此便對(duì)可伸縮性產(chǎn)生了挑戰(zhàn)，并且對(duì)可進(jìn)行有效編輯的項(xiàng)目模塊之規(guī)模做出了實(shí)際限制。然而，如果規(guī)則可在文件之間進(jìn)行傳播，即在某一文件中更新某一構(gòu)件能致使其它文件自動(dòng)更新，那么對(duì)項(xiàng)目規(guī)模大小的限制便會(huì)消失。僅有少量專門為建筑開發(fā)的應(yīng)用程序有管理參數(shù)化變更在多文件之間傳播的手段。我們把必須將所有更新的構(gòu)件同時(shí)存儲(chǔ)在內(nèi)存中的系統(tǒng)稱為“基于內(nèi)存”。當(dāng)模型大到難以存儲(chǔ)在內(nèi)存中時(shí)，就會(huì)出現(xiàn)虛擬內(nèi)存交換，這會(huì)造成大量等待時(shí)間。其它系統(tǒng)有在文件之間傳播關(guān)系和更新的手段，并且能在編輯操作期間打開、更新以及關(guān)閉多個(gè)文件。我們稱這些系統(tǒng)為“基于文件”型系統(tǒng)?；谖募拖到y(tǒng)運(yùn)行小型項(xiàng)目一般會(huì)有些慢，但是隨著項(xiàng)目文件變大其運(yùn)行速度降低的也慢。

用戶將項(xiàng)目分成若干模塊已經(jīng)是一種久經(jīng)考驗(yàn)的共享工作之手段并且限制了自動(dòng)更新的規(guī)模。參照文件往往也被用于限制可編輯的模塊。如果項(xiàng)目中的層次關(guān)系不會(huì)造成全局項(xiàng)目變更，這些操作是相當(dāng)有效的。有些BIM工具加強(qiáng)了這些限制。

內(nèi)存和處理方面的問題，將會(huì)隨著計(jì)算機(jī)運(yùn)行越來越快而自然減少。64位處理器和操作系統(tǒng)也提供了重要的幫助。但與此同時(shí)，也會(huì)有更加細(xì)化的建筑模型和更大規(guī)模參數(shù)化組方面的需求?？缮炜s性方面的問題還會(huì)繼續(xù)存在一段時(shí)間。

原文：

A problem that many users encounter is scalability. Problems in scaling are encountered when a project model gets too large for practical use. Operations become sluggish, so that even simple operations are laborious. Building models take a lot of computer memory space. Large buildings can contain millions of objects, each with a different shape. Scalability is affected by both the size  of the building, say in floor area, and also by the level of detail in the model. Even a simple building can encounter scalability problems if every nail and screw is modeled.

Parametric modeling incorporates design rules that relate geometry or other parameters of one object with those of other objects. These come in a hierarchy of relations: within object parametric relations, peer object relations, adjusting one object’s shape in response to the change of another object, and hierarchical relations between control grids and surfaces that determine the parameters of shape and placement of a set of associated objects. While within object and peer object relations update locally, hierarchical rule propagation may generate updates to the whole building. Local parametric rule propagation makes only reasonable demands on models, while some system architec- tures limit the ability to manage propagation of large sets of hierarchical rules.Also, it is hard to partition a project into parts for separate development and still manage a large set of hierarchical rules.

The issue is memory size; all operations on object shapes must take place in memory. The simple solution to manage parametric updates is to carry the project in memory.  This challenges scalability and places practical limits on  the size of a project module that can be effectively edited. However, if rules can be propagated across files, where updating an object in one file can lead to automatic updates propagated to other files, the size limitation of a project disap- pears. Only a few BIM design applications developed especially for architecture have the means for managing parametric change propagation across multiple files. We call systems that must carry all updated objects in memory simultaneously memory-based. When the model gets too large to be held in memory, virtual memory-swapping occurs, which can result in significant waiting time. Other systems have methods of propagating relations and updates across files and can open, update, and then close multiple files during an edit operation. These are called file-based systems. File-based systems are generally a bit slower for small projects but their speed decreases very slowly as project size grows.

User segmentation of projects into modules has been a time-tested way  of sharing work and limiting the scale of automatic updates. Reference files   are often used to also limit what can be edited. These work well if hierarchical relations in a project don’t lead to global project changes. Some BIM tools impose these limitations.

Memory and processing issues will naturally decrease as computers get faster. Sixty-four-bit processors and operating systems also provide significant help. There will be the parallel desire, however, for more detailed building models and larger sets of parametric rules. Issues of scalability will be with us for some time.

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