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请详细阅读有关数据架构方面的描述，根据要求回答下面问题。[说明]某软件公司欲开发一个基于Web 2.0的大型社交网络系统。就该系统的数据架构而言，李工决定采用公司熟悉的数据架构，使用通用的商用关系型数据库，系统内部数据采用中央集中方式存储。该系统投入使用后，初期用户数量少，系统运行平稳。6个月后，用户数出现了爆炸式增长，系统暴露出诸多问题，集中表现在：(1)用户执行读写操作时，响应时间均变得很慢。(2)随着系统功能的扩充，原有数据格式发生变化，又出现新的数据格式，维护困难。(3)数据容量很快超过系统原有的设计上限，数据库扩容困难。(4)软件系统不断出现宕机，整个系统可用性较差。经过多次会议讨论，公司的王工建议采用NoSQL数据库来替代关系数据库，以解决上述问题。但李工指出NoSQL数据库出现时间不长，在使用上可能存在风险。公司技术人员对NoSQL数据库产品进行了认真测试，最终决定采用NoSQL数据库来替代现有的数据库系统。请针对问题(1)～(4)，分别指出NoSQL数据库的哪些特点促使公司最终采用了NoSQL数据库。

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